one of the best ways to improve grip strength...try rock climbing! find a climbing gym nearby. if that's out of the question, try some of the following:
-one handed deadlifts
-pinch-gripping 2 weight plates together (10s, 25s, etc.)
-if you have a power rack handy, try heavy finger rolls: set the supports high enough so that you can DL a bar off them easily. load up the barbell with bodyweight (a good place to start) and DL it with palms facing out. then, let the bar roll down your hands, trying to get it as far down your fingertips as possible. play around with reps and sets.