What your bra should look like:
The strap around your body should be firm but comfortable. If it is too loose and rides up your back, you are wearing too big a back size. The wires at the front should lie flat against your rib cage and should not rub, and your breasts should be enclosed in the cups with a smooth silhouette. If there is a bulging at the top or sides, or the wires are standing away from your chest, you are probably wearing a too small cup size.
If your bra fits properly, the weight of the breast should be supported by the body of the bra and not solely by the shoulder straps. If you find that the shoulder straps dig in, it is likely that you are wearing the wrong bra size. When you are trying a bra on, remember to adjust the shoulder straps to ensure that they are not to loose.
When you have a bra on, you may need to adjust your breasts to make sure that they are in the cups properly. It’s also a good idea to try a T-shirt or top over the bra that you are wearing so that you can see the shape that the bra style gives you.