The only thing it helps with it is very basic left and right hand coordination, and timing... but having said that, the left and right hand coordination does not translate well over to a real guitar as there are no frets (left hand) and no strings (right hand) on the Guitar Hero controller.. so what little you do get from this "game" is not really all that usable. The timing is about all you really get from it..

All in all, Guitar Hero does NOT make you a better player. The only thing that will make you a better player is practising on a real guitar.