Ask me to do a headstand or nearly any other yoga arm balance, and I can do it, but I cannot for the life of me stick a handstand without the help of a wall or a spotter.

When going against a wall, I use the technique described by Yoga Journal where you kick up from a downward facing dog-like position. I can do it, but I rely on the wall to stop my feet. If I try to do it free-standing, my legs go right over!
Are there any alignment tricks, learning sequences, or strengthening/flexibility exercises I can do to help me stick a handstand away from the wall?
