What are some tips for someone looking to buy a guitar?

Firstly, the guitar should feel and sound good to you. Pay attention to different things like how the neck feels, how the pickups(if any) sound, is it light enough for your liking etc. 

 It is also important to ask yourself questions like what is the style of music I'm looking to play(heavier styles would benefit from electric guitars with  humbucker pickups for instance while electric guitars with single coil pickups would do for a style like blues), do I want to be better able to reach the higher frets( to decide if you need a cutaway or not), Do I want to be able to plug in my acoustic guitar at some point( in that case semi acoustic could be the way to go), Do I want a coil splitting option on my electric guitar( beneficial if you want to play heavy styles but also have that single coil sound).

 Also be sure to check that the guitar is in proper condition. No major damage or breakages, All electronics and mechanical parts are in good working condition(check volume and tone knobs, all pickups, pickup selector etc), No unwanted fret buzz or crackling sounds in knobs etc. It would be better to take someone who can check these for you if you are not sure.

Also make sure you get it set up so the truss rod, action, intonation are adjusted properly. Again someone who knows more about these and can verify that they are adjusted properly can help you if you are unable to make that judgement yourself.

Check hardness of the body

Check the clarity of the sound by pressing all the strings in every fret

Check the neck is straight, not slightly bent.

Check the tuning head is not loose.

Make sure the bridge is tightly intact.

Check smoothness of the neck.

Check the sound clarity.