Grip strength and forearm endurance are something that Ive been focusing on a lot lately and the results have been savage! Grip is a big part of grappling and I found it to be a weak link in the chain that was holding a lot of other stuff back.
I did lots of towel pullups, could only do 1 first (10 regular pullups) but worked my way up,
also farmers walks with a towel wrapped around the dumbell I like because I can easily mark my progress.
If you don't know what to focus on you might give it a shot! Its often overlooked by people