Usually, it's recommended that you start by fitting the largest area, and alter the rest. BUT, if your bust is a lot larger than everything else, you may have to also alter the sleeves and even the back of your dress for a really good fit. (I know...I'm busty myself.)
Some patterns come with a range of sizes included. If a shirtdress pattern you like is available in the 'flex-size' , get that.
If you can't find a suitable pattern in Flex-sizes, what I would do for a simple path to a good fit (if you're not in a hurry) is wait for JoAnn's to have the pattern you want on sale for 99cents. (This is pretty much quarterly - get on their mailing list, if you aren't already.) Buy 2 of the same pattern, one to fit your bust, and one to fit the rest of your body. GL :-)
at 12:27 PM on May. 10, 2011