In order to understand how a bra should fit, it is important to understand bra structure.
A bra consists of an area to hold the breasts (cups), a band to run around the body and hold the bra in place, a center panel, and shoulder straps on each side. Strapless bra designs do not have straps. The bra should have fastener hooks for adjustment purposes on either the front or the back of the bra. Some bra designs incorporate padding to give a look of additional fullness and lift. The band around the body should bears the weight your breasts; not the shoulder straps.