I vigorously rub the ligaments between the calf and the knee and above the knee with a rough towel after each shower.This keeps the blood flowing around the knee,which helps to lubricate it.
If your knee is swollen put ice on it every half hour or so.Then when you sit or go to bed put a warm pad behind the knee cap.
Many things can cause knee pain including arthitis,trauma,exercise. Even getting out of the car by twisting from the knee can injure it.Playing tennis is very bad for the knees because,without thinking you lunge sideways.The side motion with weight is a common cause.
I have written some hubs where I offered some remedies for joint pain.