I used a soldering iron to etch the design into the wood.
Trace over all the lines of your design slowly with the soldering iron to create a bold deep line.
At first I tried an actual wood burning tool but I found that it took way too long to heat up and got way too hot to handle after a short while.
The soldering iron heats up quickly and you can work with it for longer periods.
You'll want some goggles to keep the smoke out of your eyes. It smells nice, but it will dry your eyes out if too much smoke gets in them.
Some other instructables that discuss wood burning:http://www.instructables.com/id/Intro-to-Wood-Burning/http://www.instructables.com/id/Pyrography-Burning-Pictures-into-Wood/http://www.instructables.com/id/Laser-wood-burning-pen/