Brad's Iyengar Yoga Notebook
Viparita Karani is a Sanskrit term that refers to the "action of inverting."   Thus it is more of a general action rather than an asana and hence the name does not end with "-asana."   In Iyengar Yoga, Viparita Karani is the name we tend to give specifically to the feet-up-the wall position, although any inverting action is technically Viparita Karani and some texts will use this term to refer to Sarvangasana, for instance.   It is often called the "fountain of youth pose" because of its profound restorative effects.   Viparita karani is an inversion in the shoulderstand family and confers benefits similar to Sarvangasana, but it is easier to hold for extended periods of time for maximum rejuvenating benefits.   Few asanas have both the soothing and energizing effect of Viparita Karani.
Some poses are for doing, this pose, like Savasana, is for UN-doing.   This pose is for just being and observing.   In the restorative poses, "you don't do, you just view."   You become as acutely aware as possible of the processes of your body, your breathing, your tensions and how to realease them, and your mental fluctuations.   This pose is extremely cooling for your nervous system.   The spirit of surrender that we learn in these restorative poses is something that we should carry into our active asana work as well.
It is good to devote one entire session each week to doing nothing but this one pose.   Any fatigue, anxiety, or depression will be alleviated with Viparita Karani.   When you're exhausted from your day, it's time to go upside-down.   Aim for about 20-30 minutes in the pose if you are doing it as an entire session, but do not exceed that length of time as a general rule.
You should use a bolster or about three folded blankets for this pose, and you should be very slightly backbending over the support, not using it just to support your hips.   Mr. Iyengar had originally designed a "Viparita Karani" wooden box for this pose, though we rarely use that prop for this pose anymore (although we still use it for other poses).   Have your support about 3-4 inches away from the wall so your buttocks hang downward just slightly off the support.   This slight backbending action should not be so much that it brings any tension into your abdomen.   You want your front lower ribs at about the same height as your front hip points (anterior iliac crests) or a little lower.   You want the sensation of a lifting in your front rib and floating rib area, while your abdomen should be relaxed and sinking.   Another support you can use is two blocks (on their flat sides, end to end), with one or two 1/2 folded blankets on top of them.   This is a slightly firmer support.
It is good to do this pose on a sticky mat to allow you to tuck your shoulders a little underneath as in Sarvangasana and keep them there in a relaxed way.   This action will help open your chest.   Also lengthen the back of your head (the occiput) away from your shoulders before you begin to relax into the pose.
If you choose not to use a sticky mat, one good idea is to place a block between your bolster or blanket support and the wall to keep your support from sliding toward the wall when you are coming into and out of the pose.
If you want more support for your shoulders, you can use a folded blanket just in front of the bolster for your shoulders to rest on and allow your head to be off the blanket onto the floor (just as with the blankets in Sarvangasana).   Make sure the blanket extends to support your cervical spine, just touching the tops of your shoulders.   Without this sensory contact (Skt. "sparsa") under the neck it is more difficult for the body as a whole to release.
It helps to strap a belt around your thighs just above your knees before you go into the pose to bind your legs together so you can relax more completely in the pose without your legs falling apart.   Try to fasten the belt so the buckle is not directly on your skin.   You never want the belt buckle on your skin in a restorative pose if you can help it since that can be a distraction that inhibits deep relaxation.   In fact, when doing any restorative work, make every effort not to have your body touching anything unnecessary or uncomfortable in any way (even if it's not really painful), because that contact will generate mental fluctuations (Skt, "cittavrtti") and disturb your mind, even if only subtly.   That contact will act like a bridge to lead your focus outside your body whereas what we are aiming for in the restorative poses is to move inward.
The standard way of entering this pose is to sit on the bolster or support, lie down on your side and take both your sitting bones to the wall, and then roll onto your back, taking your legs up the wall.   Just as in Halasana, you can also roll forward into this pose from Adho Mukha Svanasana by keeping your chin well tucked and setting yourself down onto your shoulders, then rolling forward to take your legs gently to the wall.   Take care not to set yourself down on your head or neck.   To come out of the pose, you can reverse this process back out into Halasna, then back into Adho Mukha Svanasana and then relax in child's pose.   You should be quite comfortable and grounded in Halasna before attempting these variations.   Also, the main focus of this pose is relaxation, so these variations are more for just occasional practice or, for instance, for entering the pose in a crowded class where you are shoulder-to-shoulder with other students.
There are several variations for positioning your arms in this pose.   Experiment with them and find how they affect you differently and if one allows you to relax more deeply.
(1) along your sides as in Savasana
(2) straight out to your sides at shoulder level
(3) in the "stick 'em up position" with your hands overhead.   If you choose this position, keep your upper arms at about the same level as your shoulders, not much higher over your head because that position can cause some tension in your throat and neck area.
(4) resting on your abdomen.   Sometimes in a class situation, this may be your only option if there are others close around you due to a lack of wall space.
If your arms are overhead, from your feet to your hands, all the way should be downhill.   This is an inversion.
When doing any restorative pose, focus on softening your sense organs (eyes, ears, nose, tongue, and skin) -- the "organs of perception."   Your mouth should be almost open, your lips touching very slightly.   Have the sensation of unhinging your jaw so that your teeth do not touch.   Your tongue should relax onto your lower palate, not press on your upper palate, and descend back and downward.   This tongue position is key in all the restorative poses and in pranayama.   Though it may feel awkward at first, practice it until it feels natural.   Soften your throat.
One particularly restorative way to end this pose is to slide your legs down the wall and cross them in Sukhasana on the wall for a while, changing the cross of your legs mid-way through, and then to slide your tailbone back onto the floor and allow your legs to rest on the bolster crossed in Sukhasana for a while, again changing the cross of your legs.   This position is especially useful for allowing your abdomen to recede and relax.