My methodology as follows: (your mileage may vary)
#1 Perform all preventative maintenance, have it in a state of best mechanical operation. Get familiar with it.
#2 Make darn sure you have a matching diameter full size spare tire. I usually get a matching rim from the junkyard so I can rotate it in.
#3 Outfit a basic support kit- fire extinguisher, first aid, tow strap, tools, shovel, jack, emergency communication, etc. Some would say recovery points are part of the basic kit.
#4 Research any vehicle weak points or common issues, address as needed to minimize reliability risk or increase efficiency (upgrade?, attention or modification to driving style?, who knows what?). This is where I usually hit the junk yard and pick up any factory armor or recovery points my rig was not optioned with.
#5 First mod is upgrade the tires (if the vehicle has street tires). At least a mild all terrain pattern suitable for your area.
#6 Get out and hit the trails. You will find out what the vehicle asks for based on what you demand of it. You may be able to predict this right off the bat- lift, winch, rock sliders, auxiliary lights, whatever. Edit: you may find your rig suitable, and decide to spend budget on camping upgrades instead of vehicle upgrades at first. Just get out and see what calls to you.
This is great, great advice here. I get carried away in mods and "builds" but you can't forget the stuff listed up here. I kind of touched on maintenance and using the vehicle-specific forums to figure out and address the "weak points" in your rig, but JimBill makes it much more clear. I totally overlooked mentioning the matching diameter spare (that is in good shape, not dry-rotted), the basic support kit (which should also include some sort of 12V pump that is actually capable of filling your tires... a gas-station cigarette lighter pump isn't going to do a good job of filling 35"s on a heavy diesel full-sized SUV, for example), and his last point: hit the trails.
As I mentioned, I have a tendency to just jump in with both feet with my builds - doesn't matter if it's a street car, race car, side-by-side, sand rail, or what was supposed to be a mild Overlander. Don't be like me, lol.
Get your rig out there (mostly) as-is and go with a group so you can actually push it and see where it gets stuck or hung-up and make decisions based on that. Maybe you find out the clearance at stock height is fine, you just could use a more aggressive tire and real traction devices in the axles. Maybe you decide the rocks and trails like The Rubicon are what float your boat, and you'll want to do more to get your big-rig through those tighter, technical trails. I never found anything my WJ couldn't do on the previous 4" lift (front long-arm, rear stock arms with wishbone spacer) and ~31.7" tires with the stock VariLok diffs in the QuadraDrive system. Yet, I find myself in the middle of a full, semi-custom 4-link setup, hydro bumps, 3-tube bypass shocks, full frame stiffeners, trussed and gusseted JK Rubicon Dana 44s with e-lockers and 4.88s, etc. etc. etc. I don't have any regrets, and the intent is to run the Rubicon with it ASAP... but like I said I never found a situation where my previous setup let me down on the trails I was doing.
So, go out there and enjoy first. Start to get a feel for what your speed of "Overlanding" is. You'll find numerous threads on this forum, and others, debating what "Overlanding" really is, and what it means. I'll let you dig through those, by my $0.02 is it is different for every person and it should be about what YOU want it to be. Maybe it's just taking a mild dirt road out of town to get into nature in your Prius (I'm looking at you
@JCWages ) or maybe it's making it through all the winch hills at Fordyce. Either way is a-okay. Until you find what you enjoy most, and whether your rig gets that job done or not, don't go to mod-crazy (
again, do as I say, not as I do). The one caveat I'd say, is get good sliders right off the bat. Any rig should have them, but especially lonnnnng wheelbase rigs like yours. You may end up finding dirt fireroads are your speed, and you never actually needed them. But you'll be thankful you have them that one time you accidentally find a slightly more serious trail and you save your rocks/sills, doors, etc. It's a ton of work and money to fix rocker/door damage once it's done, so that is def one place to just get the protection ahead of time. Also, if your specific rig is known for having any of the pans that keep the life-blood in your vehicle (engine oil pan, trans pan, bottom of the radiator, etc.) especially susceptible to damage it's worth skidding those out from the get-go too.
Other than that, get out there and enjoy.
