Pashasana is the first posture of the Ashtanga Intermediate series and can be quite a challenge. What to focus on bind or heels down? Matthew Sweeney has some useful tips and even talks about the transition out of it.
There are the notes that accompanied the Asana Kitchen video on Pasasana.1)Establish a Grounded, Immoveable FoundationBalancing in a full squatting position is one of the most important and challenging aspects to this posture. The feet are your foundation, they are directly in contact with the earth. Organize your posture directly over this foundation noticing when/if you are either too far behind or in front of your foundation.