If, however, you need to attract some attention or are participating in a motorsport that would benefit from you making a scene, there's only 8 steps, that's not many steps.
These steps are for a removable body panel but they work the same for anywhere on the car (it's just a little more comfortable to be painting indoors).
2" Masking or painter's tape
X-Acto Knife (new blades, watch your little piggies)
Spray paint (I used Montana, quality paint, quality tips...less swearing)
Oil Based Sharpie Paint Markers
Step 1: Masking the Area
Cover the area you intend to work on with a large amount of masking tape. It gives you a surface to draw on (especially if the actual surface is a dark colour), it also acts as a stencil once you start to paint.
The iced coffee is optional but recommended.
Step 2: Drawing the Image
I generally do things freehand but you have the option of using an overhead projector to blow up a smaller image or to give you an image to trace.
Once you're happy(ish) with the image, it's knife time.
(The image is faint, but everything will be clear in the next couple of steps)
Step 3: Cutting the Stencil
Using a sharp knife, begin cutting out portions of your image. Anything that is going to be the same colour should be cut out at the same time.