I no longer use anything but a clean soft cloth on the body. Another clean soft cloth to wipe the strings down after play (in theory). Occasionally some lemon oil on the fretboard.

I used to use all kinds of thngs. Basically anything that is safe for furniture is "safe" for a guitar following the same directions. [Edit: I'm not sure about nitro finishes, but my Strat is nitro and saw a few Armour All applications with no ill effect.] Aside from being damaging that particular type of finish, the concern here is that any product residue could make future repairs more difficult, so avoid using things with a silicone base.

I used to use Armour All (silicone based) on my guitars for decades. It will not "harm" a guitar, but glueing, or painting on top of that residue might not be a solid repair. I think I was all pro-Armour All in a thread around here, but I have reconsidsered my ways.

If you are into consumerism, you can purchase a variety of products at your local music store. Most I've ever had to use lately is a bit of spit. :)