Reverse band close grips off a 3 or 4 board are great. you can move some serious weight on them.
My triceps are my weak point as well. I have brought them up recently using:
- board presses (all grips)
- reverse band presses (with and without boards)
- CG Pin presses (various heights, and with and without bands)
- Floor press (various grips)
- CG Inclines/Declines
Pretty simple, pick 1 or 2 things and focus on improving them, when they stall after a few weeks, pick another 1 or 2 and keep going.