"If you cannot perform an [asana] at a level that has allowed your connective tissue to adapt to it, you have no business attempting anything harder."
I cannot recall where I cut this from --- probably a gymnastic forum? --- but it's an apt quote for Ashtanga people.
It's also a nice idea to approach the person with whom you practice to ask what they expect from you so you're not left wondering or guessing --- or, on a more complicated level, projecting onto them your lacks and your excesses.
Jason owns and directs Portland Ashtanga Yoga.