I have used two methods. I photographed an oak door with my digital camera and used the image to create an inkjet decal, which I applied to wood areas.
I also paint them. I use a method similar to hypertex. I paint a lighter tone first, then apply a darker brown with a somewhat-dry brush.
It is amazing what you can do with varying amount of paint on a brush. Not only can you apply it normally wet, but in addition to dry brushing, which makes a transparent coat of paint similar to dot filtering, but you can use a continuous variation in wetness, and each degree of wetness can produce a somewhat different effect.