In my bra making journey, I tried (and failed miserably) at some patterns that were not my size in an era (more than 10 years ago) where the patterns mostly matched the traditional American sizing of ABCD and then you were usually told to go up in band size to get a bigger cup. I made between 10-15 bras that didn't fit and I didn't know enough about the order of alterations and how to fit bras to make them work.

About 2-3 years ago, I started to go back over my bra making information and books, and I discovered that the internet has become a GAME CHANGER for the home sewist who knows nothing about fitting. 

My curiosity led me to The Bra Making Forum which is a group on facebook hosted by a small business, known as The BraMakery (formerly ArteCraft).  The group has 14,550 members (to date) from all over the world.  Natasha, who owns and operates the BraMakery, is one of the most well read people I have encountered on the subject.  I have learned so much about bra theory and the process of fitting an existing pattern from her group.  She has recently released a pattern of her own called The Chloe, which is featured in this video below by Liz of the popular YouTube channel LizSews. 

The process that is recommended over and over to new sewists is to start by doing a breast root trace, known as a Wire Fitting, then making a fitting band and doing band alterations, then making fitting cups and doing cup alterations.  Liz makes a beautiful demonstration of this process and how to apply it to the Chloe pattern.