priming anything is mostly a matter of preference,
For dark colors I don't always prime. For models needing light colors my favorite primer over the years is still Testors Flat White from a spray can. Other people report good results with Tamiya primer gray, which I believe is laquer based - so beware of its effects on some plastics. There has been info on modeling sites about using Gunze Mr. Surfacer as a primer, but I haven't used this for anything other than texturing yet.
For figures, I tend to prime metal figures with the Testor's Flat White, but most plastics just get a brushed coat of tan or green as a first coat - which I use mostly to check seam removal, filling, etc.
There are a number of fine model sites out there, and you should be able to find good info with a quick search.
Gary