Brad's Iyengar Yoga Notebook
"Inversions cultivate the yogic mind."
-- B.K.S. Iyengar
It is often good to prepare for Sarvangasana by first doing Halasana for a few minutes to adjust your shoulders and let your blood pressure accommodate.   This also gives you the opportunity to put your strap on around your upper arms.   Measure your strap loop as one forearm's length plus the length of your extended forefinger.   Then, of course, you can adjust that loop size if less or more feels better for you.   Your belt needs to be wider in this pose then what you use in Pinca Mayurasana.
Initially you should learn to move into this pose by lying on your back and raising your legs and torso up.   It is also possible to enter the pose from a standing position by bending forward and placing your shoulders onto the floor to form Halasana and then raising your legs upward, though this is a more advanced maneuver and not often done.   For beginners, the best way to come into Sarvangasana is to swing the feet over onto a chair into Ardha Halasana, and then to come up into Sarvangasana by taking one leg at a time straight up.   More advanced students usually come into Sarvangasana by bringing both legs together (kept straight) up from Halasana, but you will need fairly flexible hamstrings to do that easily.   In general, students who have trouble with seated forward bends will also have trouble coming up into Sarvangasana with straight legs.
When you are setting up for this important pose, having a twisted strap (or sloppily folded blankets, etc.) speaks to a cluttered mind.   Take your time to get any props you are using straight and neat for they affect your pose in a direct way.
In general, this should be a relaxing, meditative posture, not a strenuous one.   You want to use more skill and less effort when holding this position.   Use as many folded blankets as necessary (even four or five is fine) to allow the posture to be more of a balance than a strain.   Aim for zero effort in the pose.   If you only use one blanket or no blankets, your hands must push your back much more strongly to get vertical.   The exception to this principle is when you are planning to do the variations of Sarvangasana (especially dropping into Setu Bandha Sarvangasana), you will want to use fewer blankets for less height (maybe two or three).   Three blankets is a fairly standard number most people use for the basic Sarvangasana.
The Sarvangasana variations focus on different physical aspects of Sarvangasana to allow certain muscles to stretch (such as the inner thighs in the Parsvaikapada Sarvangasana variation), to allow your legs to rest, and to allow you to lengthen your time in Sarvangasana without becoming too tired of one position.   Once you are able to achieve a solid Sarvangasana, you want to aim for a minimum of five minutes in the pose to begin to receive the benefits it has to offer.
It is fine to fold your sticky mat to go under your elbows, but under no circumstances should a mat be under your shoulders or your head because your neck cannot lengthen when the back of your head is on a mat.   Typically, you want to place your folded blankets with their neatly rolled sides just at the very edge of your mat with very slight steps in them to prevent them from slipping and collapsing under the weight of your shoulders.   Note that the little steps are not for the purpose of your neck at all, but just so that the upper blanket does not roll off the pile due to the weight or movement of your shoulders.   With this configuration, your shoulders are on blankets and your neck is supported by the blankets somewhat, but the back of your head is on the floor, not the mat.
It is useful to practice using a belt around your upper arms to draw your elbows inward so they do not splay out to the sides.   They are able to support your torso much more strongly this way.   Using a prop like this in Sarvangasana is specifically to get more lift in your spine, so make sure you adjust the prop so that it has the desired effect.   Remember, as noted under the section for Halasana, your feet must be on the floor (with your knees bent, if necessary) or on a chair when putting on your belt, or you can be up in Sarvangasana while doing it if you can manage it that way, but you should definitely not be hanging out in Ardha Halasana with no support for your feet while you are putting on your strap.
You can also use a chair with your hands pulling the back legs (below the cross bar if there is one) to help draw your shoulders under more deeply and pull the seat of the chair into your low back to help get your torso up more vertical.   The creative use of props to accelerate gaining "the feeling" of a pose is one of the hallmarks of Iyengar yoga.
Actions of the hands, arms, and shoulders
This pose is "shoulder stand."   Try to stand on your shoulders.   Be on the very tops of your shoulders, not on the rear part.   Rotate the tops of your shoulders underneath as much as possible and draw your arms back away from your shoulders to facilitate this action.   Lengthen the bottom surfaces of your upper arms (triceps) toward your elbows along your blanket or mat to roll your shoulders under more deeply.   Move your rear armpits toward your front armpits strongly to help move your sternum toward your chin -- this is just another way of saying to circularize your armpit chest as in Tadasana.   While being strong in this action, take care not to pull your shoulders strongly away from your ears since that action pulls on your trapezius muscles and creates tension in your shoulders.
Take your upper arms and elbows back shoulder width apart.   Do not let your elbows splay out wider than your wrists.   Take them back so that your upper arms are parallel to each other.   Firm both of your upper arms into the blanket or mat.   Only your outer triceps should be touching the blanket.   Squeeze your arms toward each other as you draw your shoulder blades together and upward toward the ceiling.   Rotate your triceps muscles toward each other.   Roll your biceps outward away from each other.
Walk your hands down your back as far as possible toward your shoulder blades to bring your torso as perpendicular to the floor as possible.   You may need to make this adjustment several times.   Place your whole palms on your back, not just the index finger sides.   Use your hands gently to encourage your spine to move forward and upward.   Use your hands more to lift your torso than to push it.   Generally it is better to have your hands on the bare skin of your back rather than on your T-shirt, but that can vary depending upon the situation, for instance how much perspiration you have on your body.   After holding the pose for a while, return to Halasana or Ardha Halasana and take your hands even further down your back a little and go back up into the pose.   You can do this several times if it helps.   If you need more friction between your hands and your back, you can even use a strip of a sticky mat especially cut for the purpose, or a sticky mat folded into 1/8ths.   Those with experience often find that they tend to push upward a little more with the little finger sides of their hands than with the thumb sides, thus lowering the fulcrum of pressure on their backs.   The lower down the fulcrum is, the better.
Press your elbows into the floor and do that specifically to lift your side ribs higher and higher.   You can elevate your elbows with a folded mat or a slant board if you feel you need more pressure on your back to get your torso perpendicular to the floor.   Generally your shoulders and elbows should bear equal weight.   There is a tendency to have more weight in the shoulders and to have the feet more over one's head.   This tendency needs to be consciously counteracted by taking more weight into your elbows, making them heavy, so that your torso is upright, heels over hips, hips over shoulders.   Getting your torso more vertical will become more natural with time.
It is also important to keep weight on your elbows so you're not feeling like you're pressing into the floor with the back of your head -- this is not a desirable action.   Also, do not turn your head from side to side in Sarvangasana.   This is simply not a position that allows much side to side movement of the head.   Lengthen your neck, but do not press it down on the floor.
As you reamain in the pose, every few breaths, adjust your hands down your back a bit more and lift up through your legs more.   Try to take your thumbs as close to your armpits as possible, and use your hands to lift your armpit chest.   Your armpit chest lifts up as your outer arms press down.   Your inner shoulder blades lift as your inner legs lift.
Actions of the torso, hips, and pelvis
In Sarvangasana, as in Tadasana, your torso and legs should be perpendicular to the floor.   There is a tendency to have the feet somewhat over the head, especially if the chest is not expanding fully into the chin.   Your suprasternal notch of your chest should move to press into your chin, not the other way around (chin moving into chest).
Unlike Sirsasana, in Sarvangasana the front of the body and spine tends to under stretch with the hips falling back and the feet coming over the head.   Be aware of this and keep your torso erect.   Open your upper abdomen, an area that will tend to be compressed.   Have more of a "Setu Bandha feeling" than a "Halasana feeling" when you are up in Sarvangasana.
Do not let your back fall down and rest against your hands like dead weight.   Keep lifting your hips directly over your shoulders.   Draw the entire back of your body in toward the front of your body and lift the front of your body toward the ceiling.
Lengthen your body maximally upward from your shoulders up through your heels and the balls of your feet.   Lift your pelvis upward, taking its weight off your torso, and allowing you to lengthen your spine maximally.   Lift your pubic bone away from your sternum.   Lift your back ribs using your elbow pressure on the floor.   Keep adjusting the pose, recharging your upward lift.
Press your outer upper arms downward and lift the sides of your chest upward.   Give length to your body from both sides of your chest.   Look at your chest with an unbiased set of eyes and ask yourself whether one side of your chest is coming forward and the other side is going backward.
Keep your chest both broad and tall.   Lift your chest upward.   This should be one of your mantras for Sarvangasana.   Retain your inner legs, knees, and ankles back, and press your chest forward and upward strongly.   Move the skin over your thoracic spine into your body to press your chest forward.   See how well you can lift your chest.   Broaden your collarbones.   Expand your sternum vertically and horizontally to open your chest as much as possible, though it is admittedly difficult in this position.
Tighten your buttocks and tuck your tailbone in as you move your thighbones back.   As you draw your tailbone inward, also turn and lift it upward toward the ceiling.   Notice that these are simply the actions of Tadasana, resisting back with the thighs, (inwardly rotating the legs), and tucking the sacrum forward toward the front of the body.   In Tadasana, your sacrum moves down toward the floor and forward, in Sarvangasana, for obvious reasons, it moves upward toward the ceiling and forward.   The same applies to Sirsasana.
Actions of the legs and feet
When we go upside-down, there is the tendency to lose the consciousness of the legs since they are no longer supporting the weight of the body.   You should pay attention to lifting your legs out of your pelvis toward the ceiling and engaging your leg muscles to your leg bones just as consciously as in the standing asanas.   Squeeze your muscles into your legs and up toward the ceiling.   Draw your thigh bones deep into the backs of your legs as in the standing poses (and counteract this action by drawing your tailbone forward).   Bury the tops of your kneecaps.
Keep your legs active by squeezing your thighs, knees, lower legs, and ankles together.   Keep recharging upward through your feet over and over each time you feel this uplifting energy begin to fade.   To ensure you are lifting both sides of your legs evenly, you may need to extend upward through the insides of your feet and legs more than the outsides.   Move the inner skin of your legs upward while moving the outer and front skin downward into your hips.   So, although the bones and muscles of your legs are lifting upward strongly, you actually want to pull the skin of your thighs downward toward your pelvis.
Observe the Tadasana of the legs.   Roll your thighs inward as much as necessary so that your legs are not rolling outward, but are centered forward as in Tadasana.   Turn your outer thighs inward and your inner knee bones back to rotate your thighs inward.   Most people do not do this action enough.
Extend upward both through your heels and also through the balls of your feet (especially at the great toes).   Broaden the soles of your feet and spread your toes as in Tadasana.   Extend your heels toward the ceiling maximally.   Raise your heels to raise your hips and to left your pelvis away from your spine.   Even though you're rolling your thighs inward and that may tend to separate your calves, draw your inner calves toward each other.   If your anatomy permits it, draw your inner ankles toward each other so they lightly touch, as in Tadasana.   This is true also for Sirsasana.
Actions of the head and face
To relax your gaze in this pose, after you have checked the position and alignment of your legs and feet, have your gaze on your abdomen or even lower on your chest.   Experiment and see that this is generally the more relaxed position for your eyes.   The exception to this rule is if you tend to have low blood pressure, you should keep your gaze focused on your feet.   Keep your eyes quiet and your forehead passive.
As an occasional exercise, you can try Sarvangasana having your mid-thighs belted together and then try to "snap the belt" by taking your legs apart as strongly as possible.   This gives you a feeling for your legs working strongly in this pose.
Roll out of Sarvangasana slowly, taking your feet to the floor softly.   Beginners should just take their arms overhead, bend their knees, look back with their eyes to try to keep the back of the head on the floor, and roll down to the floor.   Eventually you do want to keep your head down on the floor when rolling out of Sarvangasana.   One way to come out of this pose is to lower your feet down almost to Halasana, hold both your feet (taking your great toes with your fingers) and roll down slowly one vertebra at a time just until your lumbar spine reaches the floor, and then bend your knees, taking your arms overhead along the floor, and take your feet to the floor.
After coming out, one good way to relax and experience the pose you have completed is to push back over your blankets until your shoulders touch the floor and just rest there with your arms overhead in a sort of mini-backbend for a few minutes.
(2) Eka Pada Sarvangasana --
The most essential point of Eka Pada Sarvangasana is that both of your legs must be kept ramrod straight during the entire pose and while coming into and out of the pose.   This is much more important than how low you can take your leg down toward the floor.   Your upper leg must remain perfectly fixed in one place, as if you've visually glued it to one spot on the ceiling while you lower your other leg.   Make sure you keep your top leg turning inward and lifting upward.
Begin learning this variation by taking one foot down to a chair.   Bring your leg straight down in line with its tailbone -- do not let it cross over the midline of your body past your perineum (or worse).   Another important point to focus on is keeping both sides of your pelvis level and not allowing your pelvis to drop down on the side ipsilateral to your leg that is coming down.   If you are able to put your foot on the floor (or you are using a chair), draw your hamstring muscles of your lowered leg toward your buttock to help you lift that side of your pelvis.   If you do not have your lower foot on the floor or any support, then you should stretch the entire back of your leg toward your heel.
When you are not using a chair for practice, lower your leg either to 90 degrees or all the way to the floor, whichever you can achieve.   Just lower your leg as far as you can and still keep it poker straight and your hips level and spine not bending.   After taking one leg down into Eka Pada Sarvangasana, observe how red and congested it is with blood after you return it to being beside the upper foot.