In all seriousness, which is difficult for me...
A quick wipe of the whole thing, including strings and fretboard, with a dry microfibre cloth after every play. In over 4 decades of guitaring and latterly 5 of 6 of bass playing I have suffered zero grunge buikd up on frets and the like as a result.
Every 6 months or so all (gloss) painted and plated parts get a going over with pure carnauba paste wax. Matte finish paint gets a spray and wipe with a liquid car sealant, who's name eludes me.
I periodically do other stuff to fretboards, nuts, etc, but that steps over the threshold into maintanence and the brief for this thread is cleaning so I won't go there.
But most importantly Inwash my hands before playing the damn things in the first place - that's the biggest contribution we can make to 'cleaning.