It is very important that you prepare the wood surface before you paint.
This involves two different phases, the first is to seal the wood with glue
size and the following is to provide a smooth ground using gesso.
I have followed the instructioons in "The Techniques of Icon Painting" by
Guillem Ramos-Poquí. Kent: Search Press Ltd. , 1990.
Let me know if you want me to send you a summarised set of instructions.