Well for lighter woods a good basic technique I described in my last post here:
http://www.coolminiornot.com/forums/viewthread.php?tid=8961
If you\'re not glazing on top of the grain you have to be a little neater of course.
Also, you can paint quite convincing dings and scratches on wood by painting a dark line with a light line immediately under it, remembering to keep the angle the weapon will be held at in mind to get the light direction correct.
By the way if you want to simulate a bit of bark still adhering here and there I\'ve had good luck using a mix of acrylic paint with a bit of Polyfilla/spackle added for texture, this tends to dry a little lighter than it looks when wet so you might want to mix accordingly. Bark can be quite grey so simple mixes of black, white and a little brown work pretty well.
Einion