A lot of good advice here ... everybody has expressed a similar but slightly different approach. The important thing I would add is to try each technique until you find what you are comfortable with.
The MOST important thing is ... do something!
There is nothing in the world worse ~ no faster way to ruin the appearance of a model ~ than to have thick, heavy decals spanning panel lines ... especially doors or hood and trunk openings.
Makes a model look like a 1:1 car that had a sheet of plywood bolted onto its sides with painted-on flames.
There's a visual, huh?