The main thing which will help you reduce your breast size is exercise.
I know its kinda too boring to hear, but that is the fact. Since you are below 30, you can first try out yoga classes. I assure you, 60 days of yoga will have a miraculous effect on your body.
Cardio workouts are the best and natural way of losing fat from the breasts. These are also good as warm up exercises before you get down to performing the real ones.
You can do either 20 minutes of jogging, 30 minutes of brisk walking or even perform aerobics for 25 minutes. It is important to increase the intensity of your cardio workouts with every passing day.You may come across some supplements claiming to reduce breast size but they are nothing but Fat burners that WILL help you burn overall body fat but there's no way ANY pill, diet, or exercise program can guarantee you'll burn JUST breast fat because unfortunately... When you lose weight - you can't target one spot for losing fat and another thing...
You also want to consider the facts that women may see an increase in breast size when on a menstrual cycle, taking birth control pills (especially Yasmin) and when pregnant.
Do five to six sets of push ups every alternate day. Performing push ups will not only help reduce your breasts size but will also prevent them from sagging due to sudden loss of adipose tissues.If you want start with low weights first and slowly graduate to heavier ones.
Do little things around the house to increase your level of everyday activity. You can even do exercises at home like skipping and hooplas, it will help reduce breast size.
While exercising will help you reduce breast size to a certain extent it is important to take care of your diet as well. A low fat diet will help you drop sizes faster. But keep in mind that it is not possible to lose breast size without losing overall weight.
Come on, Cheer up! Follow all this and you will loose our weight for sure!