Greetings Kriegshund;
I can see the members have given you some sound advice. Essentially there are three methods for wood grain effect.
1. decals.
2. paint
3. doll house woods
Decals are my least favorite for wood grain. There is one single exception. Detail Masters has a very impressive oak grain decal listed for 1/24 scale but goes great with 1/48.
For "painting the effect" most of you have seen my efforts so here is one from a fellow modeler. His build here is an Eduard Alb. D.III (OAW).