Problem:
Band is too big.
Solution:
You need a smaller band size.
If you are wearing a 34B, try a 32C.
If you are wearing a 38C, try a 36D.
Problem:
Cup is too big.
Solution:
Try going down a cup size.
If you are wearing a 32B, try a 32A. If you are wearing a 36DDD, try a 36DD.
Band
Your band should fit you comfortably snug — not too tight and not too loose. Your band should fit below your shoulder blades and not ride up.
Cup
You cup should be large enough that all of your breast is inside of the cup and not bulging out. Your underwire should fit against your ribcage surrounding your breast and not poking into your breast tissue.
Style
Picking the correct style is just as important as the correct size. Try on 4 or more different style bras, that are in the same size, so that you can see how each one fits you differently and choose the one that fits “you” perfectly.