What should I do for my knee pain?

Strengthen. quadriceps muscles and tape your kneecap based on the direction it goes when your walk or run. This can be accomplished by seeing a sports training physical therapy program. If this isn't helping then consider evaluation by an orthopedic sports medicine specialist.
Knee pain. Pain the knee can be due to tendonitis, plica, cartilage wear, synovitis, weakness, vitamin deficiency. Just too many possibilities without a proper diagnosis. If your knee hurts, start with a basic exercise program for your hips and knees and if your pain persists, or if you feel like the knee is giving out then i would see your orthopedist.
Identify the cause. The first step is to identify the cause of the pain. If it simply osteoarthritis then medications or injectable lubricants can help. Have you doctor evaluate the knee.