Check diet, regular if not frequent farrier work, talk to farrier about options and if temp shoes (more for the radical crack, quarter crack advanced crack type scenario) might be indicated, consider way of going and the terrain the horse spends most of his time on as well as the way he stands. There are a load of oils and lotions, paints and creams you can apply to the hoof but the best bet is satisfy the dietary needs (proper amounts of iron and selenium being fairly important) and consistent/regular farrier work. After talking to your farrier and even your vet, you might find that a specific hoof supplement can help. Keep an eye out for potential white line disease if the crack is deep. I hope this is under control for you fast : )
Sure there's right and wrong but mostly there's just a whole lotta different.