Few basics
Washing every where
One famous bad spot is behind the inspection cover. Dirt and muck gets in there and ruins the release bearing pretty fast. Starters too.
If it isnt making noise just hold the pressue washer tip at the bottom of the cover and wash until mostly clear water runs out.
Its the tin cover between the engine and tranny.
Lots of grease every where you have fittings. Should be 7 on a stock setup. Anything extra from aftermarket parts needs to be done as well.
Upper balljoints 2
TRE's 2
Pitman arm 1
Draglink 1
and IIRC trackbar 1
Check all the suspension components (control arms, track bars, shocks, springs, swaybar links)
You're looking for anything out of the ordinary:
Bends, missing bolts, loose bolts, breakage, bad bushings
Engine compartment
Battery, and its holddown and connections.
Clutch fan. Should turn but be a bit stiff.
Alternator, mud and or noise
Belts/belt, wear and tension
Rad, level and condition of fins
Brakes
Most importantly for rear drums. Especially easy if you swap tires between runs.
Mud eats drum brake shoes really really fast. While you have a back tire off just pull the drum and give a quick wash in there. That will lengthen your rear brake life by a longshot.
Visually inspect all your u-joints and driveshafts. Look for missing clips, caps, or anything else out of whack.
And like the poster above said, check, and or change every fluid on your unit regularly.
Diffs are most the most common to need changing since they are low and in the water a lot.
A lot of this will just become second nature as you inspect more often, and doesnt really take that long.
Good luck, have fun.