We get tons of questions about how to take care of your guitars fretboard. We will touch on how to properly clean your guitars fretboard and how to polish your frets correctly. Before we get started if you have any doubts about the actual function of your guitars truss rod, or the condition of the frets and related playability, leave this to a qualified guitar repair shop. We can not stress that enough.
Before we outline a quick polishing and lubricating procedure, here are a couple of things to avoid. D'Aquisto felt that lemon oil, or any other vegetable based oil, could literally rot the wood as it decomposed while saturated into the wood cells and pores of a fingerboard.
He interestingly, used to use motor oil (yes, that's right, he preferred non-detergent [less additives], and 30 or 40 weight oil was fine with him). Frankly, it freaks people out when they see their repairman put a bit of motor oil on their instrument. You could also use clarinet bore oil, which is also a petroleum product available in most music stores. I figure if it can help a cylindrical, temperamental, tropical hardwood reed instrument, with someone breathing heavily through it, it will be just fine for a guitar fretboard. D Aquisto, and other luthiers, also warn against using silicone based lubricants on guitars.
When you polish up a fingerboard, here are some tips! To eliminate scratches, little dings from slide guitar playing, finger grunge etc., and light playing wear, take a small piece of 400 grit sandpaper, spread a little oil (a few drops) on it, and then lightly sand the frets across the fretboard. Then a little piece of 500 or 600 grit paper, and then a piece of 0000 steel wool, all with a bit of oil as a lubricant, and to pick up dirt and dust. Take a soft cloth, clean the surrounding finish, and carefully wipe down the fingerboard, getting any excess oil and residue off of it.
If your sanding motion is up and down the fingerboard, you will leave minute scratches in the fret that will make it harder to bend strings smoothly. Try to get any crud from between the frets, but don't lean into the wood too hard; you don't want to change the basic level of the fingerboard. If you do this a couple of times a year, that's enough. If you are a person who leaves a lot of finger grunge (it's sweat and body oil soaked dirt, really) on the board, clean it more frequently than that.
0000 steel wool leaves the frets and the wood nicely polished. If you would like to polish the frets to a higher gleam, a small buffing wheel on a Dremel tool, carefully and judiciously used with some buffing compound, can bring up a higher polish. Make sure the strings are off and well away from the Dremel tool, and don't overdo it: you do not want to heat up the fret too much. It may loosen in the fret slot, especially on a refretted guitar. Once you get everything clean and polished up restring,tune up and jam away! A clean fretboard with polished frets always seems to make me play better.