Are there any general guidelines? Are 5.1 speakers typically nailed to walls or something?
If you want to nail the speakers to the wall that’s entirely up to you. I have my subwoofer next my Mac, two speakers either side of the monitor and unfortunately due to lack of space the remaining two speakers are either side of left/right front speakers 
Hanging the speakers needs more thought; would you mind the wires showing or would you rather cover them up? Having the speakers on stand would means; you can have the wires on the floor or under the carpet.
Here is a decent guide Home Theater Speaker Layout - An Essential Guide & Reviews and News from Audioholics
Oh. Wow, I seriously always thought the extra 2 speakers go behind you and somewhat to the side, to add rear sound in FPS games. That’s not true? Only 7.1 does that?
That s exactly what I thought before buying my 5.1 speakers. I’ve seen setups where people tend to have the speakers on the either side of their couch/sofa. The setup basically fools your ears with realistic rear sound.
I think these days you can get 2.1 speakers which can fool your ears with a realistic illusion of surround sound.