depending on the surface it's applied over,mainly make sure everything is clean,sanding or scuffing will never hurt prior the application, it's best that a good 2 part primer surfacer applied before paint,but if you're working on small area,you can skip that step, and as always it's a good idea to read tech sheet or directions off the primer container ,usually you have a small window to apply top coat,if you wait certain period of time, you will have to scuff the surface