When I painted the car I made a mask out of regular masking tape. I bascially taped the windows and lights and used an exacto knife to trim the tape. Then I sprayed the outside: first with the base coat, then with the middle coat, then the clear top coat. Since getting the bit I've gotten a 1/10 MT truck and did a body with the same paint but different color. If you have the clear bit body, I would paint it from the inside by:
1. masking the inside of the windows.
2. scuffing the inside of the clear body.
3. spraying many thin coatsd of the middle coat.
4. lastly spraying the black base coat.
Note that you won't need the clear top coat. The clear plastic body serves as this. Also note that the order in which you spray your paint is reversed.
heres my MT truck
http://www.payba.net/~kolohe/newlid/