Quad stretch (yes still about knees!)
Realigning your knees .
The muscles at the front of your thigh, the quads have a big influence on your knees. If you have worn heeled shoes a lot and/or stand with your weight on your toes then it is likely that your quads are tight and can pull yoru kneecap out of alignment.
You can check this with a kneecap release.
In order to start releasing tension in your knees this stretch really helps.