What would be the best way to strenghen these muscles?

Ok, I just finished the Jennie Finch Softball Camp in Colorado and now that I have a lot more to think about and I know the correct and safe way to pitch (I wasn't that off when I was doing it before the camp) I want to know how the best and fastest way to strenghen my Arm (pitching, batting, throwing) my Core (Pitching, batting, throwing, yes you use your core in all of those) and Legs (Pitching, batting, throwing, running). I am doing the ladder excersises for now to increase my speed for stealing and running to a base. So please help, it is the Middle of the High Plains Little League season, but school season starts in 2 1/2 months and I want to be prepared and be on my A-game all season with how I play. Open to all ideas. Plus I am 12 and the closest thing I have to weights are my brothers, and his are heavy.