If this is wrong please chime in and point out whats wrong

This question comes up all the time. There is more than 1 way to do it. So I wrote down how I do it. It seems to work out perfectly.
Works equally well with automotive paints and spray can paints.

If you have something you can add to it, feel free to post it here and let me know.

To make sure your panels are oil free, like from Armour All and pooo, wipe them down several times with a wax and grease remover. If they are really Armour All'ed down, use a brake cleaner.

Get a bucket of soapy water to wetsand with.
Sand the grain out of them with a 80 grit wetsand. Get at least 75% of the grain out. Then wetsand with a 150 - 180 grit. Then move to a wetsand with 220 grit. If for some reason you are odd and like the grain look, skip that part.

Clean the panel again with wax and grease remover and also a tack cloth. I suggest wearing latex gloves to keep oils from your hands transfereing to the panels.

Spary the panel with an Adheisive Promoter. Follow directions on can.

Spray with FILLER primer. As many coats as are needed to fill in all the grain. For small items such as trim panels, kick panels and pillars, SEM makes a filler Primer that is awsome or you can use Duplicolor Grey Filler Primer. They also have a red rust colored filler primer. Avoid it. For some reason it sand horrible.

Wetsand that with 220. If you see your self going to deep into the plastic before you are happy with the finish, dry and clean the panel off with wax and grease remover and spray more primer on it. Keep this process till happy. Final wetsand with 400 grit.

Clean the panel with wax and grease remover and a tack cloth and then paint.

Spray as many coats as you like, 3 is usually plenty, and do it in light coats as heavy will clog and run and then you have more sanding to do.. Let it dry in the sun if possible as long as you can. Overnight is prefered. If you feel there are some imperfections, wet sand with 600 or more till you are happy. Clean it real good and then spray a clear coat over it. Again in light coats.

I try to let the clear coat dry for a couple days for best results.

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If doing a dash
 If you want it just painted, follow the steps above to clean and prep it and then paint it.

If you want it smooth for a glass like finish, clean and prep it as above and then lay several layers of filler primer over it. Do that in 3 steps or so till all the grain is out. Sand it smooth using the wet sand method and 220 grit. The lay some paint on it.

Now understand this..... if you push really hard on top of the dash, you can crack it. Although in all my years I have yet to see someone lay on top of their dash, or kneel on it. I suspect your dash will last for plenty of show seasons. I know people who have done this plenty and the dash looks awsome still.
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remember Armour All is the Devil.

Unless of course you have a stock interior, then it works good.

For painted peices, I use Meguiars Quik Wax after the paint is cured once a month and Quick Detailer when you want to clean it. Spray on, wipe off, flip cloth and wipe again

The only suggestions that i would offer are, not hitting the primer with anything ,more coarse than 320 since the spraybomb primer has a minimal build at best. A cheap dish detergent is excellent for the soap and water mix but avoid one that prevents "dishpan hands" cause they can contaminate the surface.
One other thought,whenever possible use a gloss paint and skip the clear. The fewer number of products the smaller the chance for a reaction between them. For cars that are not strictly show cars i would never use anything more than satin finish on top of the dash. We've had to dull the dashes in new cars for customers that couldn't stand the glare. Interior paint is typically 12 degree gloss i think. That's about as much as you want to have. in your line of sight.