I always describe dry practice as Taijigun.
Any hand/forearm exercise is a must [other exercises are a must as Vaughn will state shortly, such as running and the trunk--however, these are the ones I do for hand, finger, grip strength]. I practice exercises that my boxing club practices:
1. the windlass (3 foot dowel rod with hole in middle, 2 to 10 pound weight attached by rope [use black for enhanced tacticality]), wind down and up, palms down, palms up, one palm up and other down while in horse stance, 10 times each.
2. the lever (3 foot dowel, but hole 1.5" from top), rotate hand in semi-circle, left to right and right to left, 10 times. In addition, move bottom of rod to weight and back. In both exercises attempt not to let weight move.
3. fingertip pushups, lots of them. Hold in down position to strengthen hands.
4. Panther and Tiger push ups. Panther is also called "hand crawling" where one "hops" forward, back and side to side. In club we hop in circles--it is no fun!
5. Phonebook toss [Vaughn's right, this one will make your arms bark]. Take Indy (or wherever) phone book, wrap it in duct tape (another use for this miracle product!). Toss with one hand, catch with other. Catch with palm and wrap fingers around. With partner and alone.
6. Coin pick up. Take 50 nickels, put on table, get in horse stance, pick up nickels quickly as possible, place in other hand without dropping. If drop, have to start over! If going too slow, instructor will make you start over. Groan.
7. Reverse curls and forearms curls with long bar, add weight with progress. Can also use dumbells.
8. Sand bag toss. Get bag about 14" by 14", fill 1/3 with sand (more later), toss with partner. Can also use bag for iron skin and backstop to clear or dry practice. Can be done with partner and alone.
9. Brick catch. Take cinder block [I use a rectangular piece of concrete like a stepping stone in a garden, start with something lightish and work up], drop from shoulders while in horse stance, clap hands and recatch while falling. Warning: watch your toes those first few times. [Can use a jar filled with sand as well. Fill jar, grab with fingers at top and carry around with you--helps to be bachelor as sand can have negative impact on carpet and wifey's 'tude.]
I work out with long guns. Excercises, militree presses, lat raises, curls, etc. Just holding pistols out with one hand helps. I still do pencil shooting, but I use a 1911.
Hope this helps. Let me know if you need any further info.
*EDIT: inserted comments and typos after Vaughn's post and I forgot about the jar thing inserted in brackets.