Learn as much as you can.
Read plenty of off roading magazines and books. I had a nice book about 4x4 and it gave plenty of info on crossing streams, sand, slush, approaching angles, crossing gaps, rolling over the obstable with the tire instead of trying to get stuck on the undercarriage, etc. Learn some basics.
Go to some 4x4 classes if you have them. You will meet other folks who may not be rock hounds and boonie bashing, but are their with real SUV learning how to use them in a track setting under controlled conditions. They are not ther to crash and crush their SUVs but learnign how to use them for realistic adventures.
Join a local Mild Ride club. Join local explorations where other folks use their SUV for exploring on trails, go to scenic destinations, and mild offroading. IF things go wron,g you have a group to help so you won't get stranded.
Get some basic things like replacing the crappy Dunlop/Bridgstones with BFG AT, a shovel, chains for snow, 3-4 inch wide towing straps, maybe even a snatch block or pintel hook to get unstuck, an air compressor to air up and down, a nice thick piece of plywood about 1 foot square to allow the jack to be placed in soggy, mushy ground, a Pull-Pal type of self digging anchor to get unstuck.
There's a lot to make an already capable 4Runner even more capable without turing it into a beat up rock crawler.