| Here's usually what I do. On a new instrument with a virgin board I use two coats of Watco Natural Danish oil, the first coat goes on and sits for 5 minutes and then gets wiped off with good cotton rag, then a second coat goes on and is wiped off after a minute or so. Pay attention to the surface after the oil is wiped off, there is the possibility of "weeping" where more oil oozes out (usually around the pores) and needs more wiping otherwise it collects on the surface and looks crappy. On old boards I first clean the board with Naptha (use gloves) and a piece of gray scotch brite, then wipe clean with a paper towel to get off the dirt and finger funk that builds upon the board and the frets (you'd be amazed how much crap comes off), then I put a coat of oil on and wipe it off after about a minute following the same procedure as above. I’ve done about 7,000 fingerboards this way and had nothing but good results. I hope this helps. | 
