Step 2: The Sketch
Sketch up whatever it is you wish to burn onto the wood, on some tracing paper. No need to make it overly detailed at this point but if you want to add the detail to give you a better idea of how you wish to burn it, go ahead. .
Once this is finished, place the carbon paper on the wood (carbon side down), and the tracing you did over it as you wish it to appear on the wood (as you get better with the iron OR if you are able to make decent sketches directly onto the wood, these steps will be able to be skipped). Retrace only the outlines and major portions of your sketch, so that a light carbon copy is made on the wood. This becomes the outline to follow.
The horses head is how I "want" it to look when finished. The second picture is of an example of another burning I did, and this was the outline on the tracing paper.