Sorry I’m late to the party. How you clean it / what you clean it with depends on the finish and what material the fretboard is and just how “gunky” it is. When I have something absolutely disgusting to clean, I’ll use an old toothbrush and Simple Green or equivalent cleaner on the fretboard, but make sure you clean all the residue after. You can also use naptha (lighter fluid) and a soft rag. Either way, make sure its dry afterwards and then if its a bare wood like rosewood or the like, treat it with a boiled linseed based oil, don’t use lemon or any other citrus based oil, it’ll dry it out and Crack it. Body of the guitar might be “good enough” with just a soft rag or microfiber cloth, but be careful, its easy to pick up debris and completely scratch it up. You can also use a guitar polish here, but don’t use furniture polish, it’ll just create a waxy buildup that will never clean off 100%. As far as metal parts go, chances are they’re played, and this plating is very thin, use caution if you use any kind of polish here. I’d avoid that and just get the chunks out with a soft bristle brush, and if the adjustment screws on the bridge or anywhere else are corroded or rusty, put a couple drops of pfte based lube (sold here as “superlube”), or if you’re in a pinch you can use 3-in-1 oil, but be prepared to have a ton of paper towel on had because it will make a mess. If your tuners are sealed "most likely they are) don’t bother trying to oil them, they’re not designed to be. Hopefully this helps!