Quickly, step one is an introduction tank set up with sand and some rock that looks like a mini reef - here the fish can learn to eat food and not be afraid of you. Having a friendly fish in there to show them how to eat pellets or mysis works great. 40 breeder works well for this. Fish do not leave here until they rush out when they see you and eat pellets or flake. Step two is real ocean live rock with diverse microfauna that will eat parasites as they fall off of the fish - reef and introduction tank. Dry rock and fresh sand tanks are petri dishes for ich tomonts. Step three is to lower the stress on the fish in the tank, and the largest part of this is having places for them to totally escape and hide - going into a cave or arch is not one of these places and if you can see them, they are not likely secure enough. Feeding enough for the fish to grow is the other important step. I do dip some wild large angels for flukes.
I haven't have a spot on any of my fish for over a decade. Eating well. Feel safe. Healthy fish. It works for me.
Some fish don't care about hiding. For the ones that do, like tangs, angels, triggers, etc. they will be more healthy if you just stack up rock and let them get totally out of sight.