Here's an exercise to help strengthen and coordinate your bow hand.

Notes about the video:

"You want to focus on having a coordinated, "group" effort from all you fingers--no divas! If one or more of the fingers on your right hand is doing their own thing you'll have problems--particularly check your thumb and your pinky--no locked or hyperextended knuckles, make sure they're rounded and flexible--relaxed. Let me know if you have more questions. "