Check for rust as it can be expensive to repair. Common locations are,
1 Rockers, which are made up of 3 sections running the length of the lower body.
2 Wheelwells where the fender and the wheelwell meet, particularly at the top of the front wheel well and where the rocker ends are.
3 Ends of the X frame under the center body where it meets the inner rocker.
4 Front mounts for rear springs.
5 Rear spring mount itself usually stands up but the integral chassis leg can rust out on either side causing loss of integrity.
6 Front and rear floorpans where they're spotwelded to the x frame and around the edges. Dirt and water can get trapped underneath.
7 Windshield frame lower corners on series 3 to 5 will rust but you can't really tell unless you remove the glass and weatherstrip or it's really bad.
8 Lower front and rear fenders rust.
That about covers the most likely rust area. You can find it in other places but usually not as bad. Of course if your find is from the south or west where rust is unknown then so much the better.
Now as for mechanicals, blocks can crack near the generator/alternator mounting holes if proper coolants have been neglected. Rear ends will whine and if it's never been apart it should be disassembled to have thr ring gear bolts replaced. The lock tabs on them compress over time and the ring can loosen potentially causing a failure. Wire wheel hubs, if it has them, wear out, particularly if they haven't been greased. transmissions last fairly well although you find some that pop put of gear during deceleration due to worn gear hubs. Nothing really to be done about that right now.
Weatherstrip dries out and should be replaced. The windshield seal particularly becomes porous and lets water through.
Check to see that the wiring harness doesn't appear to have been messed with. Rewiring isn't difficult but will cost 250 - 300 dollars for a new harness.
Interior, with the exception of original floor mats can all be replaced if needed.
That's about it off the top of my head. If you have any questions I'll see what I can come up with.