I just LOVE wooden effect cake boards! They suit all kind of cakes. You can adjust the wooden effect to your cake by simply changing the shades of colours used for painting the board.
Roll out some icing. You can use some leftovers from previous cakes as long as the colour is a little lighter than the colour you are going to use for the board.
You can use a bit of water or glue to stick the icing to the board.
Place the icing on the board.
Smooth the surface with a smoother.
Using a knife cut off the excess of icing.
Once again smooth the surface...
... and the edges.
To mark lines I use a ruler, but you can use whatever tool you prefer.
Using a wheel tool mark lines as shown on the photo.
To paint the board I usually use three shades of brown. To get different shades of brown you can mix together yellow, white, red and blue in different proportions (more white in lighter colours). I use dust colours dissolved in alcohol.
It's quicker to use a wide brush to apply the first layer, but you can use whatever size of brush you have. I start with the darkest shade of brown.
Remember not to over-soak the icing with the colours - it will take ages for the board to dry! ;)
Remember about the edges.
The first layer doesn't have to be perfect.
Use a smaller brush to apply some lighter shade of brown.
Using a wider brush slightly blend in the lighter shade. It's important to use a dry brush, so that the colour doesn't blend in completely.
Repeat previous steps with the lightest colour.
Add some black to your leftover colours and use it to paint the grooves.
Dry the board overnight so it hardens before placing the cake on it.