Weak muscles are the leading cause of knee injuries. The best thing you can do for your knees is strengthen the surrounding muscles. The most effective knee strengthener I’ve found for my knee injury has been an ailment practice in the standing yoga pose, tadasana.
Start by lifting the toes off the floor. Turn the tension in the feet inward, which will engage muscles in the leg. Visualize the inner thighs circling inward toward the back thighs. You’ll feel a tension in the outer calves.
I learned to do this in a yoga class, and I continue to lift my toes whenever I think of it. My knees have never been better.