Rest, ice, compression, and elevation are four of the best initial treatments for knee pain. So for the first 24 to t48 hours after the pain develops, stay off your feet as much as possible, prop your legs up on a aoullow or two, wrap your knee snugly but not too tightly with an elastic bandage, and apply cold packs to the sore joint for 15 minutes every hour.
For icing, a bag of frozen peas wrapped in a thin towel is probably your best bet since you can easily mold the bag so that it conforms to the shape of your knee. In addition, if you feel tingling or numbness or see discoloration in your foot, loosen the elastic bandage because it is probably wrapped too tightly.