About twice a year I do the 'fingerboard job': I tape off the f'board between the frets with that blue 3M lo-tack masking tape and use a very fine grade sanding sponge to shine up the frets, followed by steel wool to get that mirror finish. I'll run a toothpick (although those bamboo skewers work better and are virtually unbreakable) at the foot of the fret on each side to collect that crud. Then I pull the tape and put the lemon oil on and let it soak for about 20 minutes. Then I wipe off the remainder, new strings put on, tune, check the action/harmonics (waste of time, my neck has not appreciably moved in five years), and play the stretch out of the new strings. Done, it feels great!
J o e y