got a new one for you guys

unless it's pre-sanded (never seen one that was) you need to sand it. you don't need to use more primer unless the surface is scratched or damaged (primer is a filler).

if the surface is perfect, you can simply use a scotch pad to scuff up the surface, or you can use the more conventional method of wet sand using 600 grit. being an undertail, you won't have to stress minor imperfections

you may use a sealer if you want; it can help reduce the amount of basecoat you need in order to get an even color. most sealers do not require sanding prior to applying the color if done within the recommended flash time, however if you have dust specs or inperfections, you will want to lightly wet sand to even it out (600grit or finer).

apply the color, using enough coats that the color is even, waiting the recommended time between coats (depends on type of paint, temp, and humidity).

if all is good, you can apply the clearcoat, or if there are some imperfections, we sand before applying the clearcoat (you will have to give more time for the paint to cure).

between all steps, use compressed air to blow it dry and remove any dirt, then go over it (lighty; don't apply pressure as even if the paint seems dry to the touch, the paint underneath may still be wet and using pressure will cause imperfections) with a tack cloth.

make sure you don't paint in cold temps, and make sure the paint is room temp - this will reduce the amount of problems you run into.

a note on sandpaper grit: 600 grit if fine when wet sanding prior to applying topcoats (when using enamel and clearcoat I use 400 grit). if you're afraid of cutting through the topcoat, higher grits will take longer but may give you a bit more leeway. wet sanding with 1000 grit and higher is primarily for smoothing out imperfections in the paint (dust specs or "orange peel") prior to buffing - 1000 grit for machine buffing; finer grit for hand buffing.