I clean my grips once a year usually. Use a dishwashing detergent (like Dawn or something similar) and warm water, scrub with a soft bristle brush, then rinse, then wipe dry and let them air-dry out of the bag for a few hours.
Never had an issue, unless the grips are so worn that they need replacing. And if it's the multi-compound decade grips/half-cords - after they air-dry I'll take a light-grade sandpaper and rough up the cords a bit so they become a little more tacky.