You'll need to match the type of primer to the paint that you're going to use (over the top of it). For example, if you're planning on using enamel, use an enamel primer. If you're going to use acrylic lacquer, use an acrylic primer.
You can usually get away with spraying enamel over an acrylic primer, but not the other way around.
If you've got access to a spray booth, you could consider 2 pack.
If you have some larger scratches or imperfections, you can use a 2 part automotive filler. There are primer fillers and spray putties as well, but unless they're 2 pack, they don't have very high builds and they tend to shrink back over time... revealing the imperfections again
