How to make a body board less slippery?

Use dishwashing soap. A brand new decent bodyboard usually has like an oil-based finishing on the top... so the best thing to do is to get dishwashing soap and gently wash the finishing off... you'll feel the difference. That way, when you're droping in on a wave, you don't go slipping right off. You should also make sure you use wax on the board. I usually use "sticky bumps" wax.