i think u might want this tutorial, so here is it
1. i make a rough sketch using normal softairbrush on a perspective line. i use mazda savana blueprint as references.
2. after i got some preview on the car, i start to render the BG. just do light brushing on the lower layer from the car and follow the perspective line.
3. i start the lv.1 tracing process to get clearer view, reduce the car skecth opacity, create new layer above it and starts brushing with sharper brush.
4. i do color testing first before i do enhancing on the line and color it so i can get a guidance. just brush the skecth with some colors possible.
5. now i start the 2nd tracing process, i reduce the car sketch once again and create new layer above. i use 1-3 pixels penciler brush to get cleaner and sharper line. the result is almost the same with mechanic pencil.
6. after we got the clean linework, make a new layer bellow the line, and do grayscale shading like i always do. need a few pracice on this.
7. create a new layer above the grayscale,pick all colors on the "color test we created before" and splash 'em to the grayscale, change the layer mode to "color", we need to add some highlight, create another layer and set it to overlay mode, and brush the hi-key area with bright colors. don't forget to do the BG.
8. do detailing on BG per object, road, horizon, fences, wall, gravitty, etc.
9. we are almost finish now, just add sveral effects such tail light glow, flare, smoke, etc. i create the tail light glow from right to left to make a perception that the car change it's line from right to left with smooth movement. adjust the color with some color adjustment and masking and we are finish with this.