Usually I just stick the beans in a glass jar with just enough properly ph'd water to cover the seeds, and keep in a warm, dark cabinet. Then, I plant the ones that crack-open. (a sign of viability) The seeds usually crack overnight, but sometimes they take a day or more longer. Exchange water daily with fresh, properly ph'd water. Check them daily. Once cracked-open, the clock is ticking twords the seed drowning.

Some of my tougher beans get the sandpaper and paper towel method. I use fine sandpaper (220 grit or so, but a matchbooks striker works too) to lightly scuff some of the waxy coating off of the seed to promote easier absorption of water through the seed's shell, (forcing it to crack-open) and I can keep adding moisture without drowning the beans. But if you let 'em grow till the taproot starts showing, the fine roots may snag on the paper towel, which can be a death sentance to the seed.

Avoid over-handling the seeds when ready to plant. Easy to contaminate or break the delicate roots. I use hemostats or tweezers, but again...use care.