Depending on where it's been and what I had in the tank should greatly influence this decision. Assuming the worst for the rock and the most delicate of tank inhabitants. I'd rinse, spray, submerse and soak in clean water over and over again. Possibly bleach, dry and start over again with the rinse, spray and soak for good measure. Then after all that and always before setting in my tanks. I take some water change water from the tank a cup of sand or preferably a small rock, a powerhead and seed the new over the course of a few weeks.
While some may recommend other things and they certainly may not be wrong. I'm always wayyy over caution with rock. Too many crevices for nasties to lodge themselves in.