Specifically, you can train:
-ulnar deviation of the wrist
-radial deviation of the wrist
-pronation and supination of the hand
from sledge levering and nail bending. Most people don't train those types..
Wrist flexion and extension are the ones usually trained.
You can work these by many things. Some examples could be wrist rollers, wrist curls, etc.
You can get loads more information from grip sites. here's a couple popular ones:
gripfaq.com
gripboard.com