First you sand to solid paint or bare metal depending on what you have to start with. The first class guys go down to bare metal. next we prime with epoxy (2 wet coats) no sanding between coats unless you have bug-a-boos..Then we do the blocking and any filler work (you did do any metal repair did you not) once we are satisfied the body is straight then we shoot a seal coat (epoxy primer works just fine) no sanding unless you have buggers in the seal coat. then we shoot the base coat (enough to get full coverage) Most base is just color and does not shine. then we shoot the clear coats 2-3 coats of that to full coverage.
Your results may vary according to the skill of the painter
I have tried most all of it and now do what is known to work..