I've said this many times, but I'll say it again, forearm curls are a great exercise. Low weight, high reps. The game is played at the extremeties, and everyone is willing to do calf raises because they think it'll lead to dunking, but strong forearms beget quick snappy handles, ball control in traffic, better on ball defense, quick release on jumpers, improved range, and will snap off passes quicker and with more range as well.
The actual skill of passing is a little different. A box on a wall is a great target. Jason White Chocolate Williams talked about throwing 500 passes a day against a wall target with each hand on the move, behind the back, and just about every other variation you can think of, in an interview a hundred years ago.