The biggest question is to base or not to base. Most of the metallic glitters on this site don’t need a base. For the most part, they’ll stay their “true color” regardless of whether or not you add a basecoat to your project. This is because the metallic glitters are totally opaque with regards to their color. The colors do not show anything thru them and the only reason you MIGHT want to base coat these colors is to avoid having to put on a second layer of glitter in case your first coat doesn’t cover as well as you would like. If you did this, then what would show through is the color of your base coat, so choose a base that matches the glitter pretty closely. But, with the awesome coverage of S&C glitter, this is generally not necessary.
As for the other colors on the site (the iridescents, the fluorescents, the mattes, etc, etc) they generally DO require a base coat as they are more translucent than the original sparkle. For this reason, you can sometimes manipulate your final outcome somewhat by doing a complementary base coat that will match your glitter or is slightly darker or a slightly different shade than it would be if you did your base coat in a neutral white or black.
If you’re unsure about what category the glitter you purchased from S&C falls under, you can go search on their website and once you find the color in question, if you click on it, above it it will show you exactly what category it falls under. This will help you in determining if your glitter is original sparkle, or another type of glitter (matte, iridescent, fluorescent, etc, etc)
The other big question that is asked is what type of base coat to use. In general, a flat paint is best, be it acrylic paint or spray paint. Yes, it’s possible to base a cup with acrylic paint, but if the paint is a light color, it may require several coats of paint to get good coverage. If you’re only planning on doing a white base coat then it’s best to spray paint. This allows slightly more even coverage and can be accomplished in only one or two coats.