If you only get one thing right about a safari, make it the guide. The camp decides how well you sleep. The guide decides what you see.
They find things you would drive past
Most of what's out there is hidden, still, or the same colour as the grass. A good guide is reading tracks in the dust, watching which way the vultures are circling, noticing that the impala are all facing one direction and have stopped eating, and hearing the alarm call that means a predator is moving. By the time you see a leopard, they have usually known something was there for ten minutes.
They know when to wait
This is the real skill, and it's the one that separates a guide from a driver. Anyone can take you to a sleeping lion. Knowing that this lioness is going to get up and hunt in twenty minutes, and being willing to sit there through those twenty minutes while other vehicles drive off, is how you end up with the morning everyone else missed.
They use the radio, and ignore it
Guides share sightings. That's how word of a cheetah travels across the plains in minutes. A good guide also knows when not to join the convoy, because eleven vehicles at one cheetah is a worse experience than one vehicle at a hyena den nobody else has found.
They read behaviour, and explain it
Why the elephants are nervous. What the giraffe is doing with its neck. Which of the two males is about to back down. The animals are interesting to look at and they're fascinating once somebody tells you what's happening, and that commentary is most of what you'll remember a year later.
They position the vehicle
Sun behind you, engine off, at an angle that doesn't block anyone else and doesn't crowd the animal. It sounds small. It's the difference between a photograph and a silhouette, and between an animal that stays and one that walks away.
How to tell before you book
Ask who your guide will be and how long they've guided. Ask whether the same guide stays with you the whole trip, because handovers between parks cost you continuity. Ask whether they're the driver as well, which is normal in Tanzania and fine. And when you're out there, tell them what you care about: birds, photography, big cats, sitting still. A guide who knows what you want gives you a different week.
What they can't do
Produce animals on request, and drive off-road in a national park, where it's prohibited and the fines are serious. If another vehicle is cutting across the grass towards a cheetah, that's a guide breaking the rules rather than a better guide. Ours will stay on the track and find you a better angle from it, and we'd rather you knew why.