I'm not expert but I'd always say look everywhere for rust, and just general stuff you should look for when buying any car. Have a search on here and even Google I'm sure I found a list of problem areas when I was buying mine a few month back
Noises from the front suspension, lower ball joints are a common fault. Miss-fire while revving, indicates coil packs are poked or on their way out. Noises from the diff, or power steering pump usually signs that it has had a hard life doing O's.
Other than that, just go for one with a factory airbox over a pod filter.