The handles on most clamps are round in cross section and quite smooth. Shiny things may sell well, but when it comes time to bear down on clamp screws, slippery handles make it difficult to transmit strength. Wrapping the handles with cloth friction tape is an easy and effective solution.
The tape is made of cotton cloth impregnated with butyl rubber making it tacky on both sides, though it does not tend to leave adhesive residue on tools or hands. It is quick work to wrap the handles in a simple spiral pattern as the tape adheres to itself and to the handle. The enhanced grip will make you feel like you’re Popeye after he downs a can of spinach. (For younger readers, that means like a ball player on ‘roids.)
Some handles are impractical or unnecessary to wrap, such as those on my Jet parallel bar clamps. When I want to torque up those, I use rubber palm gloves to make the job faster and easier. These gloves are also a big help when pulling horizontally stored boards at the wood dealer.
I bought the friction tape, $2.50 for a 30 foot roll, and the gloves, about $7.50, at my local Ace Hardware, though both are widely available.