If you're using proper handgrips like the CoC ones then mix it up a bit.
Warmup on an easy gripper than you can do for ten reps, do a set or two of 5 reps. Then move to a challenging gripper you can only do for 3-5 reps and do a couple of singles. Then move on to your max gripper than you're trying to close, and do a single with maximum effort.
After this do a few sets extra stuff with some submaximal grippers. This can be inverted closes (turn it upside down in your hand and close) or holding it shut for time, you can do sprints on the treadmill closing the grippers, do some bodyweight exercises like squats while closing the grippers, work them into circuits, try and get a certain number of reps in a time limit, get people to slap your arm around while doing closes, tempo closes...theres millions of different things you can do.
Also don't discount training your weaker arm, and also training other elements of grip ESPECIALLY extensor training to balance it out and make sure you don't get problems. An easy way to do this is get an elastic band around your fingers and open your hand against that resistance.