Here are some tips from my personal experience to help prevent or alleviate knee pains.
* Wear knee straps during soccer games and trainings. Knee straps reduces strain on the Patella Tendon. I bought my knee strap from Walmart.
* Wear knee pads regularly. Knee pads keep the knee area warm (especially in winter times) which could help tissue healing.
This post seems to indicate that use of Glucosamine and Chondroitin most likely have no effect in treating Osteoarthritis of Knee.