Look at your picture and decide if you reached out to touch the real thing which bit would you touch first (on a dog its usually its nose) once decided that will be the thickest part of your intarsia and all the other pieces will be lower for a 3d effect (the bit furthest away should be around 5mm thick)
Brian i'm a bit stumped as to how to make certain bits stand out , do i just keep sanding the other bits until they are thinner than the prominent ones , sorry for such newbie questions , i dont have a belt/disc sander at present , so i would probably have to do it by hand