How to start body work.

[AmadeusCharger500]

I'm doing one door. I would like to hear some methods on how to get the door ready for a first stage of paint. Primer that is. Im starting over on this project but would still prefer not to take the door entirely down to bare metal. Lets say Im at the point of breaking the old paint to a point of finding any imperfections and breaking through so a layer of primer will adhere. Whats a typical process? send me to a book if you like Im open to any and all suggestions. I've painted one car 8 years ago so I have some small level of skill.

Thanks