Place the stencil on a work surface and airbrush the basic flame outlines. Paint the outlines in dark red, using a 0.2-mm nozzle for the edges. If you can draw, simply airbrush the flame shapes onto your canvas the way you want them to appear. This may be a single flame, or it might be a single large flame with smaller flames trailing off.
Attach a 0.4-mm needle to apply yellow spray paint at the front center of the flame. Airbrush the yellow thicker at the center and have it fade as you bring it back toward the tails of the flame. Switch to red paint and spray over the lighter yellow on the tail end of the flames.
Paint dark blue paint at the core of each flame with even strokes until you have filled in the base of each flame with the blue paint. Leave a little of the under color showing through to give the impression of real flames and the way they burn.
Spray around the outline of the flame with either yellow or a very dark red to thicken the flames and to give them depth. Since flames burn at various colors, mix various shades of red and orange to give the impression of a realistic flame. Add touches of white to the ends of the flames to give them a little smoke effect. Keep the smoke lines minimal and light.