This fantastic video from Bravissimo shows exactly how to escape from the Bra Matrix and get a bra that looks good and feels comfortable ! It shows what do the words "well-fitted bra" mean; and they also have a step-by-step guide for you to do it yourself. If you are among the 80% of women wearing the wrong size, do check it out. For motivation, I have posted my before-and-after boob photos.
What the video misses is something about the migrating bust tissue and the way you have togather it into the cup, so go read about that here. It is vital to getting the right measurement and keeping the boobs in great shape.
For those of you who prefer the tape-measure to the mirror, here is my post on measuring for the correct bra size.
Photo by Lidia Camacho