this is the best way of doing things:
clean it with a degreaser to get rid of all armor all and such...

then sand the dash so it is no longer shiny (this will take awhile - be patient)

clean it again - thoroughly, so there is no dirt or grime left on dashboard

you are taking the dashboard completely apart, right? you're going to need to repeat the process on vents, etc, too.

you will need to prime the dashboard and vents for best results...

then paint...

its a long process, but if you take your time and do it well, it will turn out really nice... just be prepared for the glare with the white! it's killer!