Using water based acrylics, start with a light color that you would see in the type of wood you wish to replicate. Brush it on the part fairly heavy, then dab a darker wood color around over the light color randomly, then brush gloss clear over the whole part, this will smear the colors together creating the woodgrain effect, and leave a varnished like finish. Because acrylics shrink 300% as they dry, the detail of the part will not be sacrificed. Practice this on a scrap piece of plastic, you'll soon get the look you want.
