I: Ice. Ice the injured area. Do not apply ice directly to skin, use a towel or cloth to wrap it in. Icing will help reduce swelling and ease the pain. Ice for a maximum 10 minutes, then no ice for 10-15 minutes, then ice again for 10 mins, etc.
C: Compression. You can use a flexible bandage to add pressure to the injury. Compression can help reduce swelling and stabilize the joint. Make sure bandages are not so tight that they cut of circulation.
E: Elevation. Elevate the injured limb (above heart level) to reduce swelling.
If pain and swelling do not subside, or if you are unsure about the seriousness of the injury, seek medical attention.
It is a good idea to pack a first aid kit with you for sporting events or outdoor recreation. Include cold packs/instant ice in your kit.