i used to spray skips but ive done plenty of my own cars and done a good job too, what ive allways done is rub the filler down with 80's and then everything with 320's, prime any filler you have put on and anywhere you have rubbed through to the steel then rub the primer down with 320's when its dry, after that blow all the dust off, panel wipe it, tack rag it then spray it