Decide where the graphic will go on your car, and sketch the placement on a sheet of paper. Note the size and dimensions of the graphic. If the graphic will be seen from multiple angles, draw each main angle. For instance, if you are creating a flame that wraps around the front of the car and extends to the left and right side panels, you should draw a design lay out for the front and both sides.
Draw the design out on paper. Create a basic frame of the design first so that you can layer elements over it later. If you are drawing flames, you can create curved lines for each flicker of flame. If you are drawing something like a skull, then be sure to mark out the guideline for the skull with an oval. You can add ovals for eye sockets and a triangle for the nose hole.
Fill in the details on your design. To flesh out a design of flames, draw curved parallel lines around each guideline. Taper the ends of each flame so the flames come to a point. Add details like teeth to a skull with two rows of small rectangular shapes under the nose. Ink all of the lines that you wish to keep. Let the ink dry, and erase the pencil lines.
Color you design before sending it to a decal company. You can do this with art markers. Use orange and yellows for the hottest parts of the flames and slowly add in red to create a transition of color as the flame extends. If you are coloring a skull design, use blues and grays around the eyes, nose and teeth to give the skull some extra shadow and detail.
Scan your design into your computer at 300 dots per inch. Upload your design to a custom decal company like CarStickers.com or DecalJunky.com. These companies will take your image and re-size it to your specifications and send you a custom graphic decal. All that is left to do is to carefully apply the decal graphic to your car.