Check out the Maintenance section of the Frequently Asked Questions.
Here's a quick random list of some things to check/service (there are more):
Anything that takes grease (driveshaft slip yolks/U-joints), replace all gear oil,
all filters (fuel, air, oil), distributor cap, rotor, PCV valve and grommet, Valve cover gasket, distributor O-ring, Oil pump cover gasket if you have a leak (front lower engine), flush cooling system, refill with 50:50 distilled water and anti-freeze, clean Throttle body, clean/lube all rubber weatherstrips, lube all hinges, remediate any rust on undercarriage components/body, inspect brake pads/calipers, apply cavity wax (3M) to internal body cavities, disconnect, inspect, clean harness connections (CRC Electronics cleaner), disconnect, clean, reinstall all grounds, complete fluid exchange (transmission), rear axle rebuild (seals), inspect emergency brake (components), inspect/replace throttle cable, service fuel injectors, ----
Spend a few hours (days, weeks, months, years (

) reading through this thread and links:
The Frequently Asked Questions (FAQ) for the 80/LX450 series tech section continues to be a work in progress. The goal is to have links in the below to other threads and tech articles. By having these linked, instead of pasting the text, the threads will remain live. The live threads can...
forum.ih8mud.com
Post up some photos of your engine bay, oil pans, and undercarriage