I use automotive primers, Tamiya's surface primer, or Army Painter matte black, whether the top coats will be oils, enamels, or acrylics. All three primers work well to provide "tooth" for the top coats. The only caution I can think of is to make sure the primer is cured before starting applying colors on top of it. And as Del mentioned, make sure the piece is cleaned well. I use a couple drops of the automotive de-greaser SuperClean in a pan of warm water to wash a figure or a kit, whether resin, metal or styrene.
Hope that helps, prosit!
Brad