I got a deal on a used Epiphone Les Paul Classic for $400 AUD. The pictures I've got of it are good, no scratches or dents anywhere. I'm going to go check it out soon but I need a song that can test it's capabilities and sound. I am only a beginner so nothing too hard.
My Gear:
Epiphone Les Paul Standard
Peavey Vypyr 30
DW Collector's 3 pc drums
Mapex Black panther snare
Sabian AAX/Zildjian K cymbals.
Just play the guitar the way you usually play and something your familiar with. Play with the tuners, detune it and tune it back up so you can feel how the tuners are. I got an Ibanez once that had a bad tuner and I didn't realize it until I got it home it was in tune when I tried it I replaced it but finding one single matching Ibanez tuner was a pain. Work the toggle, Vol and or Tone knobs and listen for noise. Are you going to be getting a new amp soon? I would bring my amp with and see how it sounds thru that if you plan on keeping it for a while.

I take a small tool set with me and I remover the cavity cover just to see if the electronics have been messed with and if they were I like to see how well the work was done. That might be a bit much for someone just starting out.