Apart from get your general fitness as high as possible,since having your heart rate through the roof,will not help accuracy or decision making. Shuttle sprints are the most relevant to paintball ,all explosive activity .What you can practice is holding the squat position and rotating positions round a bunker standing position. If you have a gun you can practice ,switching hands ,snapping up to a shot off the break.Both moves are automatic to a seasoned player but require honing your muscle memory. You can practice knee,hip slides ,crawling down snake with your gun up.Whenever you practice anything,even fitness work ,always with gun in hand .You can shorten the learning curve considerably by being comfortable with the basic moves of paintball,leaving your brain free to concentrate on shooting and comms. The internet is full of vids to help Try Tech PB,Planet Eclipse and Marcello Margotts school just for starters. Subscribe to PB Acess for hundreds of game vids you can both watch and listen to pros commentate.This means when you finally take to the field you will be as prepared as possible "Fail to prepare,prepare to fail".Nothing will guarantee sucess ,it will make failure less likely!