Work on your arm speed an how fast you "flick" your wrist. Also REALLY good accuracy would help so you know that you wont hit anything you didn't mean to! Not sure it's the BEST way but it worked for some of the pitchers that were on my team. Our coach told them to do it and now the person who's playing up is our best pitcher! Hopefully it will work for you!
Of course you always want to get your arm warm and keep it warm. But the best advice I can give is work on your arm with out your power (legs) practice throwing the ball on your knees. Then when your nice and warm stand up and put your power into the pitch... Good luck!