Ice it...but also heat it up with a heating pad too.
Google some knee strengthening exercises...there are 2 or 3 that seem like a waste of time but I started doing and kept at them and I think they work...
One is just laying or sitting on the floor one knee pulled back and one leg straight...all you do is lift the straight leg up...it works the muscles around knee as you lift the leg.
Another is putting something like a foam roller under one knee and doing a 'mini' leg lift of about 6 inches (from the knee down...you do not lift the whole knee...thus the foam roller) again it seems to work and strengthen the muscles around the knees...and they stabilize things and cut down on pain and other issues.