The most important thing to remember with a fast break team is that you can pass the ball quicker than any of them can run up the court.

I would advise alot of transition drills like 3 v 2 then 2 v1 or a continuous 3 v 3. Also simple pass and go drills like the 4 corner passing drill. My favourite give and go drills are just take a 3 v 3 make it into a nice small area, say anywhere inside the 3 point line to the baseline is what i usually do. You condition it so there is no dribbling. You can't make a shot before you have completed a set number of passes and then let them make up the rest of the rules. Allow them to be a bit creative with it because it isn't the most interesting drill.

Transition time is obviousy very important to a fast breaking team but if you add good give and go passing to the team then they'll fly away from teh defenders.

I would also try to have a set passing movement for a fast break. My team aren't fast breakers but they know what to do when they are. We go from the rebound to the outlet, SG/SF (varies on who rebounds obviously but assuming it is the PF/C) who is stood on the wing at around free throw line extended. To the midde to the PG who can either drive to the hoop or wait for the support to come from the wings.