Hmmm, I've never done one...but I would imagine the colors used would be directly related on what type wood effect you are trying to achieve.
If you are looking for just a 'wood' look, maybe you can start off with a black base with silver marble, and apply a mix of candy red and candy pagan gold. This would give you a darker wood.
OR, apply a silver or copper base with black airbrushed wood grain, and then coat with the same candy mix as above.
If you are just looking for a simple wood, just mix up the brown of your choice. Then take some a coarse sponge and spray some black on it and smear it over the brown. Airbrush some knots in it.
Just some ideas for you!