First scrub it out thoroughly - it'll probably hurt a bit for your cat, but you have to get completely clean first, so you might want to secure your kitty so you can work on his paw with out difficulty. Then try some iodine, I've used it before and it does burn but it's effective. Wrap up his wound and clean it every day (maybe even twice a day), but don't use iodine every time - peroxide or some other anti-infective should work just fine. Also try to keep him from walking on his paw too much and check his paw constantly for litter and dirt. If you don't see an improvement in five to seven day then he needs to see a vet.
Good Luck
Good Luck