First of all I figure out WHY the horse is biting....then take steps to fix it. If he bit me because of something I did, well, I simply say ouch. It's MY fault I got bit so the horse shouldn't be punished for my mistake or lack of attention. Now if a horse is biting out of dominance I start with ground work to establish respect. I don't allow him near me for awhile, and if he does manage to get me I'll back him up until the look on his face changes. Not aggressively, no yelling, but assertively, back him up. I never, ever smack a horse.