Painting plastic (resin) garden gnomes -

[Adsos Letter]

3. There are primers designed specifically for your situation.

They are usually water-based acrylics with exceptional adhesion.

Surface prep is usually a simple cleaning (make sure to get any detergent residue thoroughly rinsed off) and a very light scuff sanding with something like 220 sandpaper. With some primer products simply a good cleaning is enough.

Edited to add: on plastic a product like one of the water-based etching solutions is better than sanding. I'm thinking of JASCO's "Paint Etch" product, but there are others.