Put the bottom layer of flames on, then give it a coat of clear. Scuff up the clear and apply shadows. I use an airbrush with over-reduced paint, allowing me to build up the shadow gradually. If/when you screw up a shadow, you can easily wipe it off with reducer without touching your flames. Squirt another coat of clear over the whole mess, scuff it up, and put on the second set of flames.
Hope that helps.
