There are a couple keys to getting a good faded paint look. I primarily do armor, but I think this can apply in a lot of circumstances:
1. Spray a very dark primer. I spray all my armor pieces a solid flat black.
2. Spray on the top coat, but allow the black to show through--slightly. I do this by "dotting-in" the color--kind of like spraying overlapping polka dots. It takes time to do this right, but when done, your paint already has a mottled and faded look to it.
3. Put a little white in your base coat, mix thoroughly, and start over with the overlapping dots, except this time concentrate your efforts on side panels and other horizontal surfaces that would receive continued exposure to sun, wind, rain, etc. I try to focus on the centers of panels; leave the edges darker--don't spray your lightened base coat there.
4. Do a dark wash around all raised detail after putting down a gloss coat. This will keep the wash from "bleeding" into surrounding paint--unless that's the effect you want.
5. Start drybrushing using an even lighter shade of your basecoat (add more white), and then end up with an even lighter color. I like colors like radome tan, and armor sand.
Try it, and watch the detail "come alive"! Hope this helps you some...
Gip Winecoff