I sit my rattle cans out on the windshield wipers on my car for about 10 minutes. The area around them is black, and the windshield soaks up a lot of sun. Brings up the can to a very nice warm temperature for spraying and makes it flow nice and smooth.
I also use the same location as a drying rack. I'm usually ready for recoats in minutes when I'm not wet sanding between coats.
Candies are always a challenge regardless of whether you have a proper gun or a rattle can. As always, prep, prep, prep. And always try to eliminate or minimize sharp edges. Paint naturally wants to flow away from them, and with a transparent or candy coat, will show less color.