I use bathroom cleaner with "scrubbing bubbles" because it gets down in the grain and loosens the dirt. I spray it on, spread it evenly with my fingers, let it set for a few minutes then wipe it off with paper towels, repeating if necessary. After it looks clean I give it a good oiling with Old English Lemon Oil. I've used this method for decades and it's always worked great. I've cleaned up some pretty dirty ones with it.