Ideas for exercise at the gym: stationary bike and elliptical trainer are easier on your knees. Don’t jog, run on a treadmill or do step aerobics.
Glucosamine worked for me and there is some medical evidence that it helps but it takes 3-4 weeks of taking it every day to start to feel better.
Warming up helps a little but more for muscles than joints. There really is no stretch for knees.
To build the muscles around your knees try doing leg curls (front quads) and leg presses – but if it hurts your knees even a little don’t do them!

Glucosamine does help, so does regular massage, eating right and getting proper water and nutrition.

To prevent injuries do some gentle stretching, before exerting. Also before you exert, make sure you have proper shoes and perhaps a brace.

I bet the best cardio for a bad knee is swimming, or anything else in the water. Most kicks for swimming strokes you don’t even bend your leg (or barely) and the water displaces any shock to your joints making it no impact BUT water also gives great resistance. Water sports are perfect way to get in shape at any fitness level.

Swimming is the best without putting stress on your joints.

The best cardio workout for a bad knee is the swimming pool. All those Olympic swimmers on tv look pretty fit.

get a strechable band and tie it to your door take steps forward and back and it all bout control

elliptical

Why don’t you start by swimming.
Yes join the Y. I use elliptical – but it’s preventive.
My knees are fine now and I know elliptical is better than running, since it is no real impact.

I also bike.

But I don’t know what effect biking or elliptical would have on already-injured knees.

I think I can safely answer with respect to swimming but with respect to everything else, you need to ask your doctor.

I have the bands but that gets real boring real fast.