would help to know what vehicle it is (some have trouble spots that others dont), but heres a general run down:
all suspension and steering components! these wear extra hard on offroad vehicles.
stuff like wheel bearings, ujoints, transmission fluid (for an auto), clutch condition, brakes (esp the drums adjusted if you have them)
id have all fluids replaced (diffs, tcase, trans, coolant, power steering, brake fluid, oil)
other than that, follow any recommended service interval stuff, if youre due for a timing belt, do it.
PCV valve, replace it! its like 6 bucks and will save you alot of headache cleaning out dirty intake runners!