Years ago when I first got into this hobby, I began learning things and amassing a bit of knowledge, which I then used as a opportunity to start a similar thread. Bodie took the ball and ran with it hard -- you can see it here:
Newbie Guidance
(You can stop at the first page, in fact after Bodie's response -- the following pages are just folks rightfully thanking him for his insights.)
A couple more things I've learned since:
-- This can be a VERY expensive hobby. Be mindful of that, especially if your rig is your daily driver as well.
-- Skid plates are the most important mod I've done to my ride.
-- Do you really need that RTT?
-- It doesn't take much of a hit to the rear axle for there to result in an insane cost for what seems like virtually invisible damage.
-- If you're trying to surmount a sketchy obstacle, don't be too arrogant to ask your passenger to get out and help you navigate. (Also better to not have your wife in the car should you flip over.)
-- The console safe is a great investment.
-- So is the tow hitch hide-a-key.
-- Spend less time on this site than on the trail. Some people seem to post so much, so often, and so instantly respond, I wonder how in the world they find time to drive around the block, much less parts unknown.
-- Don't underestimate nature. Learn about it. Igneous rock and sedimentary rock behave very differently; understanding that may save your life. Frazil ice is scary and kills lots of people every year. NEVER trust sand, snow, nor mud just by the looks of it.
-- Nature changes very fast, especially in the mountains. One time in the Tetons, we went down what seemed like a simple, largely flat, beautiful fire road off the highway for a short, impromptu jaunt. The weather was perfect, sunny, not a cloud in the sky. Literally five minutes down this bucolic road, it started dumping rain. The bucolic fire road instantly turned into mudslide. Thankfully we were able to turn around and very tenderly make a terror struck retreat.
-- Do you really need that snorkel?
-- Once you get your roof rack, and eventually that RTT (you know you will), don't take your car to the automated car wash. The machines have been known to rip the rack right off many a rig.
-- Bears are everywhere. They're really smart. And always hungry. Use bear bags. Even if your food is in your rig, inside of a fridge or cooler, bears will tear your car open and feast. Nothing to make you wet your bed, when you're sleeping in that RTT like the sound of your car getting smashed open by a bear lured by your strawberry scented chapstick.
-- Do you really need an auxiliary battery? YES. As well as a trie deflator kit and an air compressor. Airing down tires will get you through most of the basic obstacles. But don't air down too much, so make sure you have a digital tire pressure meter so you know when you're at the limit.
-- Go SLOW. Like real slow.
-- Wheeling while hungry is dangerous.
-- Do you really need that winch?
-- Make sure you learn how to use your hi-lift jack, winch (yeah, you might need it at some point), CB radio/sat phone, etc. when you're at home -- not at some dire moment in the middle of nowhere.
-- When you ignore, neglect or just plain forget all of these bits of advice, just have fun.
I could probably list a hundred more things. But so much of the glory of adventure is figuring it out on your own. No amount of other people's insights will help
you figure out how to not slide off that mud bank or avoid rolling over on that cliff or when you should just turn around and not trying to crawl over that rock.