The golden rule: be ready before the truck is
A farm vet's visit succeeds or fails on preparation, because an animal still out in a big field when the truck arrives burns the visit's best hour on catching it. Catch the animal well beforehand and settle it in a pen, yard or stable it knows, with a halter on if it wears one and a companion nearby if it is a herd animal that panics alone. Shut the dogs away, and if the animal is hard to handle, say so when you book - vets plan their approach and their help around honesty, not around surprises sprung on them in the yard.
A space the vet can actually work in
Choose ground that is level, dry and easy to clean, with enough light to examine by - a vet peering into a mouth or at a wound in a dark shed is working at half strength. Check that gates swing, that the crush or race runs if you have one, and that there is a water supply within reach for washing down. Keep the area clear of machinery, bales and clutter, and if you suspect something infectious, pen the animal apart from the rest and tell the practice when you book, so the visit can be sequenced to protect other animals, including the ones at the vet's next farm.
Have the animal's story ready
Vets work from history as much as from hands, and a vague 'she has been off a few days' wastes the sharpest tool you have. Before the visit, write down when you first noticed the problem, how it has changed, what the animal is eating and drinking, what its droppings, milk, eggs or breathing have been doing, and anything already given or tried, with the dates. Note whether herdmates are showing anything similar. A helper who can hold the animal, and another pair of hands for gates, means the vet examines rather than wrestles, and the whole visit stays calmer for the animal.
While the vet is there, and after
Ask your questions during the visit, not from the yard gate as the truck leaves, and write down the instructions, the follow-up dates and who to phone if things change, before the details cool. Confirm what to watch for that night and what would count as a turn for the worse. Then record the visit - findings, treatments, next steps - the same day, while it is exact. KinsLe's Pet Passport is built for exactly this: the animal's records sit in one portable packet, so the history you hand over at the start and the notes you take away at the end live in the same place.