Today I'm using the front of an old drawer that I picked up at my local reStore for a buck, they will hang as isle markers in my parent's pet shop. Once you've sanded, primed and painted your piece, go online and search out pictures and clip art that you love, you can even experiment with fancy fonts. Please be sure that you aren't infringing on any copyright laws. You can use a basic word processing program to resize your graphics to whatever size you need. I'm using a couple of sheets of paper to get them to the right size for my "canvas."
Turn the page over and cover the design area with chalk. It doesn't have to be a thick layer, just use the side of your chalk.
Now place the paper, chalk side down, on your chalkboard in the location you wish to drawn. With pencil, pen or stylus, trace over the drawing.
When you lift the paper you'll have the perfect template to work from. Just go back over the tracing and color it in to your liking.
Now go...go cover the world with chalkboard paint!