Boy this is a good question with a zillions ways to go. If it was an airplane lots of procedures before first start. If ones training / mechanical skills / time and money are unlimited then... before starting... start at the top of the long list.
I get the deal one can't wait to hit the road or trail and you could ... if feeling very lucky. What do they say "an ounce of prevention is worth a ton of Excedrin pills"
Fuel is very important. Location where once stored too. Diesel is very susceptible to algae. One doesn't want to suck that thru the system and then have to get crazy on a flush to work it out of the system.
Batteries. Have GOOD quality batteries. Electrical gremlins can be found in "new to U" surplus rigs. Checking over all the wiring with an understanding of what it does and connects to would be nice. Many times wires are cut, parts missing, requiring more Excedrin's.
Tires, wheels, hubs, brakes very important too. Don't let the year and mileage fool you.
Lube chart would be handy to follow along. All fluids engine, transmission, diff's, brakes, etc.
Being a Hummwv and for all the years in storage, it is good that your thinking where to start... prior to starting. Just know it didn't come with a dealer prep. package... so your're the one that it falls to.
Anything one misses will likely come back to bite one in the butt...so do your best now. Also a good time to learn the "in's and out's" GOOD LUCK !!!
It's part of the hobby and I'll let the gang here advise, CAMO