welcome to the forum.
not sure if your question is about prevention or treatment looked more like how to prevent...
prevention is easy via quarantine but no guarantees as ich ro velvet can still skip Qurantine as cysts might come in with LR or corals... or fish can still carry disease with suboptimal qurantine so most of the time it's about improving health and immunity of the fish so they can live with it.
qurantine is of course key
choosing healthy specimens
feeding quality food and boosting with vitamins.
reducing stress by minimizing fish known to fight.
keeping tank paramenters stable especially temp, PH, so fish stress less.