I have an old magazine article that covers this exactly. I'll have to see if I can scan and post it for prosperity.

Check for rust in the fenders, especially the rear. That is usually the first place they start rusting out.
Check underneath and see if there is rock rash on anything. If you see scrapes on the bottom of the axles and along the frame chances are someone was pounding on it a bit. You might also want to check the transfer case and make sure the mounts are in one piece. When you take off the transfer case shifter should have very little movement.
Listen for various noises. If the transmission is making more noise in 3rd and 5th, but not 4th, the bearings are starting to go out and will need to be replaced at some point.
There really isn't to much to these little rigs, so there isn't to much to go wrong.