Before the truck arrives
Have the horse caught, groomed enough that mud is not hiding the hoof, and handled by someone the horse respects. A farrier should not spend the first twenty minutes being the person who finds the horse in the back pasture.
Tell them about the last visit, any lost shoes, heat, abscesses, or a limp before they unload. If a veterinarian is involved, say so. The foot and the medical plan need to match.
The place they work
They need level, dry footing, light, and enough room to step away from a hoof. A barn aisle with a sweep of loose hay, a slope, and one bulb is a bad place to ask someone to stand under a horse. Shade matters in a Florida summer. A windbreak matters on a Kentucky ridge in January. In a Texas lot, think about where the horse will stand when the ground is either dust or mud.
Tie the horse the way the farrier asks, or hold it if that is the plan. Dogs and loose horses are the most common reason a visit goes sideways. Put them up.
The horse's job in the appointment
A horse that will not stand, that leans, or that kicks is a safety problem, not a personality quirk to surprise someone with. If your horse needs a more experienced handler or a different setup, say that when you book. Some farriers will not work on a horse that is dangerous, and that is reasonable.
Teach the horse to pick up a foot on an ordinary day, not for the first time when someone is under it with tools.
When they leave
Walk the horse after the visit. Ask when they want to see the horse again and put it on the calendar. Pay what you agreed, including a trip fee if that was part of the booking. If a shoe is lost the next day, call them with what you see rather than waiting a month.
Keep a note of the date and what was done. That record is what the next farrier, or the vet, will ask for.