On Rosewood, I've always used guitar cleaner to clean the fingerboard. I clean it each time I change strings. Every 3 months or so, I'll clean the board, then use Pure Lemon Oil to condition it. I put a little bit of the Lemon oil on the board, work it in a bit with my finger, let it sit a few minutes, then wipe off the excess with a clean, soft cloth.( it only takes a SMALL amount of Lemon Oil !!! ). On a really dirty board, you can use some 0000 steel wool, to help clean it, and shine the frets. Just tape over your pickups with some masking tape first !!! Then, lightly go over the board with the 0000 steel wool ( this is ULTRA FINE steel wool ). Clean the board afterwards. I buy the Lemon oil at a Hardware store. It's the same stuff used on Fine Furniture, etc... Make sure it's Pure Lemon oil. The Brand I use is " Old English " . Comes in a big bottle, lasts a long time, not expensive. *** As Kent said, the Dunlop products are good, too. They just weren't around back in the old days. So...I've grown used to doing it this way over the years.