That sizing chart on your favorite shopping website isn’t just there for decoration. Once you get a grip on your proportions, you can (and should) consult it to ensure you arrive at the perfect fit.
You will need:
A soft tape measure, like the ones used for sewing
A pencil and paper for notes
Underwear and a bra (so measurements are more accurate)
A can-do attitude
Twenty Tees Viscose Lycra Tank Dress ($98) in Black