Look at what you are doing right now when it comes to your knee. Are you sitting down with your knees bent? Are your feet crossed? Are your feet behind you and under your chair?
All of these positions put greater stress on the knee, leading to irritation of the knee, which leads to knee pain.
The happiest position for your knee is when it is straight. As the knee joint bends, greater stress is put on the joints and ligaments. Basically as you bend your knee, your kneecap presses against your knee, leading to anterior knee pain. If your knee is bent, you increase the tension in the ligaments in the knee, such as the ACL, which can lead to ligamentous knee pain. Lastly if you have internal knee pain, the greater the knee is bent, the more it puts unnecessary stress inside the knee joint.
If you sit in this bent knee position for hours, it will progressively make your knee pain worse.
Quick Fix: While you are sitting at your desk, on the couch, in a meeting, or watching a movie, remember to keep your knees straight when you can to decrease stress on the knee.