So what I do is paint the whole region to look like the wood all over the model. So, for me, that's dryad bark, followed by a heavy bulb oil wash, then a Gorthor brown dry brush.
I then usually check the rune area and apply more wash to the recess, so that's it's really dark and gives a good contrast.
I then did fine line of Loren green outside of the rune. I leave the recess alone, so that it remains a super dark woody cookout. Then highlights of I think Straken green. I then go back and tidy up with a fine detail brush and dryad bark.
Fairly simple, the only bit where you really have to be careful is no getting any paint in the recesses as this will diminish the effect massively.
Hope that helps.