AFter you have applied the Spot Puddy and have sanded it down you will now be able to spray the primer.
After you spray the primer, you will want to take some black spray paint and mist a "guide coat".
A "guide coat" basically tells you when to stop sanding. Basically, when the black is gone, STOP. This will let you get rid of high spots in the primer. Here are some pics of the primer with the guide coat applied.