Go read the CGN Gopher Shoot pages (and pages....). It'll give you some ideas of what you can expect.
Keep in mind that you may know some of the people you will be dealing with, for the rest of your life or theirs. If you want to come back and deal with them, that is. You'll meet some good folks!
Accept that some folks are not that keen on another fella asking to shoot on their land, mostly due to poor experiences prior to you. Don't be the prior experience for the next guy to have to suffer for!
Be aware of livestock, fences and gates.
Bring a screwdriver that fits the screws that hold the heater fan in. Hard to get the windows to defog, when their is a half dozen cases jamming the blower!

(true story, that)
Bring clothes to handle some weather, both really hot, and really cold. And rain gear. Sunscreen and Mosquito repellent!
Maps. Maps are good. See if you can find a Land Owner map for the County you are going to go to or are in. Aside from the names of the owners (maybe ex owners, depending on how current it is) you see where the local roads go, and get a pretty good idea what the land is like (Crown, Private, Range Leases, etc)
Check out the area on Google Earth. It'll give you an idea of the land use again. Range usually is good for gophers, wheat fields, not so much (visibility sucks!).
Call on friends! Make some new ones! Hooking up with like minded folks that know the ground around the area, is gold!
Ammo! Bring lots! I don't need the speedloader, but I tend to keep three loaded mags in my pocket, and swap out a mag and top off while scanning for the next targets. Gotta relax a bit too. Never had a bad day out.
Cheers
Trev