Since your cat will take care of most of his cleaning needs, you should really only need to bathe him once in a while, when he's really dirty.
When it's time for a bath, place a mat or towel on the bottom of the sink to keep your cat from slipping and make him feel more at ease. Run a few inches of lukewarm water into the sink and dampen the cat. Work a small amount of cat shampoo over his body, but avoid getting any soap (or water) into his ears, eyes, or nose. Then, thoroughly rinse his entire coat with warm water. This is especially important, because your cat will wash himself after the bath and will surely lick up any shampoo you missed. After rinsing, wrap him in a fluffy towel, dry him off, and be sure to keep him away from any drafts until he is completely dry.