What he said. make sure the paints are compatible and that the temperature is right for the paint (not to humid). Light coats work best too.
sand, primer and paint. make sure the nozzle is facing the helmet. paint lightly, several coats.
Depends on what style helmet your doing. I did ROTJ and used spray paints that Lynn posted on here. Search for helmet paint and you will find the list.
I was wondering the same thing. just got my first bucket and wanted to know what color spray paint to use if any.