Salamba: with support
"One of the most important asanas." ~B.K.S. Iyengar
The best way to understand the progression of this posture is to refer to Iyengar's book, Light on Yoga. He explains how to get into the posture and (more importantly) the way a beginner's mind feels during a headstand. Teachers can often lose sight of how scary & confusing this pose can be.
Interlace your fingers nice and tight so the palms can cup. The crown of head only touches the mat and the back of head touches the palms. Snuggle the knees in close to get ready. The distance between the head and the wall should be only two to three inches. "The weight of the body will be felt on the elbows." ~ Iyengar
Walk the toes in close, round into the spine, and lift one leg up. Secure the leg onto the wall and then lift the other leg up. Ideally, you want your legs to be between two corners. Otherwise, your tighter side will try to overcompensate and pull the body to one side. Eventually, you want the legs to be straight when coming in and out, but in the beginning bent knees are fine. I like to have my students stay with the feet on the wall for months; there's no need to rush this posture. With time, they can really connect to that feeling of the vertical lifting from the elbow points through the plum line of the body and up through the feet. The body and mind will know when they are ready to move away from the wall.