One thing that really helps is to make a template.
I made some templates for my emblem on my Kabal. I drew the shape out in paper, cut them out like paper dolls, then just used the form and a pencil and lightly followed the template on my vehicle surfaces.
The nice thing about the paper templates is they can "form to fit" whatever surface they are on.
Once you have traced the form, just fill in with paintbrush by hand.
_________________The Dread Pirate Garness
Visit my occasionally update blog