You dont have to have the going down stairs stuff.
I just have going up stairs and thats what the Doctors Told me.
Seriously, I find it funny that we are all chicks posting on this topic.
Try some of the excersizes.
Its usually caused because your inner thigh muscle isn't as developed as the rest.
I know it sounds crazy like "Well..I walk..i exercise i do blahblahblahblah".
So do I, but since we are female, we have hips, since we have hips, our legs tent to turn inward which causes your kneecap to rub in places it shouldn't.
So..
To help that, do a bunch of stretches.
Like..
Sit down, with your leg stretched out and reach for your toes (flex your toes wile doing it)
AND/OR,
Standing *you should hold onto a nearby wall so you dont lose balance* Take your foot, and bending at the knee put your foot up to your hip, hold for 15 seconds then relax, then do the other foot.
Also sitting down, putting weights on your ankle, and then lifting up your leg works beautifully *no more then 2 pounds to start, then work your way up to 5 pounds*
Also, putting it in a brace *like..an Ace bandage, is supposed to help a LOT.*