That depends on what you're trying to do. From your message header it sounds like it was hurt. If that's the case it's best (IMO) to give it a chance to heal or it'll just get worse. If you're just trying to strengthen it check out the target training section for a whole list of movements. I messed one up several years ago and being hard headed, kept working it till it got to the point I couldn't work out at all and it took about 2 months out of the gym to let it heal. A lot of people don't do enough compound moves but instead use a lot of isolation movements. Beef the shoulders up a bit and the strength and endurance will come and also help avoid injury.