Stretch your IT bands HEAVILY....
Strengthen your VMO. TKEs work... squats with someone between your legs that you're squeezing (or wall squats with a pillow or something).
Basically get the medial side of the leg stronger and loosen up the lateral side. Strengthen the hammies.
The tendency of some patellofemoral syndrome is to have the knees collapse in when they squat.
Pretty much what Dave said though.