Preparing the surface
Choose a well ventilated area to work within. Outdoors is best, but an open garage or basement will suffice. Put on a surgical mask to prevent inhalation of dangerous fumes.
Prepare the surface you will be painting by sanding with 300-grit sandpaper.
Apply a primer to the area you will be painting. Allow to dry per manufacturer's instructions.
Apply one base coat of paint in a color that will provide a nice contrast to the flames. Allow to dry per manufacturer's instructions.
Painting the flames
Cover the entire area you want to paint flames on with masking tape.
Draw your desired shape of flames onto the masking tape.
Cut out the shape of the flames by scoring the masking tape with a utility knife.
Spray the bottom of the flames with a red spray paint. Spray the middle portion of the flames with orange spray paint. Spray the top portion of the flames with yellow spray paint. Allow to dry completely according to the manufacturer's instructions.
Remove the masking tape and reveal your flames in all of their glory.