Whenever you have an ache or pain in the knee, hip, back... whatever- listen because your body is trying to tell you something. It needs RICE.
Rice is not a only the foundation of good sushi. Its also the acronym for the foundation of good training. Follow the letters to help avoid injury, especially if you are working your body harder than it's used to.
Rest- muscles need a chance to heal the microtears they incur from exercise. Its the rest and healing that make it grow stronger.
Ice- Ice packs reduce the swelling. Feels good too :)
Compression- wrapping the injury or sore muscle reduces swelling and provides necessary support while its healing.
Elevation- Keep it up and keep off it for a little while. Keep the blood from pooling in it.