Mine only got bigger once I transitioned... but hmm, wonder if that had anything to do with the fact I was miserable and put on 70 lbs? I didn't notice that they either grew or shrank on T, but losing 50 lbs in the past 6 or 7 months has made them a decent bit flatter... now I just have to deal with the fact that, even though they're mostly just the breast tissue itself at this point, that's the hardest part to bind.
The only tip I have for you, then, is lose weight, if you're overweight or if your breasts are mostly fatty. You can't decrease the breast tissue itself without surgery, but you can minimize the filler, per se. Don't do pectoral exercises under any circumstances, as Josh mentioned... bulking up your pecs will only make your tits stick out further. Just cut back on high-calorie foods, eat more veggies, drink more water, and the rest will follow. Also, binding will help to not shrink, but flatten them... but it depends on your own body as to how much it will and how long it will take. I've been binding over 3 years now, but it's only been in the last 6 months or so that I've noticed them flattening. Hope this helps a bit.
SD