I know that in dance and general correct posture, you want to always make sure the center of your knee cap goes directly over your second and third toe (from the big toe) during movement. The knee is a pretty unstable joint so always watch for alignment. Check out how you walk/run, too. Your feet should always line up with your knees. If your feet go outwards (knees inwardly pronated) when you walk/run, your knees are still going forward and it torks your knee joint. Same thing if they go inward (knees outwardly pronated). There are several ways to correct that habit. One is to constantly check out where your feet are in relation to your knees when you're sitting or standing. Line 'em up! Another way is to walk slowly forward towards a mirror (so you can see what you're doing without looking down) while trying to keep your knees and feet going directly forward (insides of feet shouls be parrallel, not outsides). Try walking backwards too. Knee bends are also a good idea. Standing with your feet in parrallel and hip-width apart, take a slight bend and keep your knees going directly over the second and third toe. Don't let your knees roll in and touch each other or roll out away from each other. Repeat the bends.

Having improper alignment in your knees can cause all kinds of problems besides screwed up knees, like a sway back which can cause lower back pain. Having knees that turn inward can also press your arches towards the floor, contributing to flat feet. When you start to correct these kinds of things you should do it very slowly. You'll be using muscles that you aren't used to using. If it hurts, back off and make smaller changes. If you've got some serious pain or a major injury, see a doctor before messing with your knees any more!