A good bra does half the work. There are many bras available that will make your breasts look bigger. Buy a Wonderbra, Miracle bra or a padded push-up bra. Don't be afraid to ask the lingerie sales consultants for assistance. It will prevent you from buying an ill-fitting bra.
If the bra still doesn't give you the results you want, buy some bra pads. Bra pads are usually made from foam or silicone and come in different sizes. Some bras come with special pockets where you can insert them, but you can also place them in the bra cup, under your breasts. They increase your bust size immediately
A little Hollywood magic goes a long way. Apply blush between the breasts to suggest shadows and deeper cleavage. Make sure the blush is a shade darker than your skin tone. You can even add some shimmery glitter on top of each breast to highlight it and make it appear rounder and fuller.
Wear a tight Lycra top or sports bra over your bra and under your shirt to add an extra layer which creates the illusion of bigger breasts. Wearing horizontal stripes helps too. They trick the eye to think that you are fuller on top than you really are.
Exercise to strengthen your chest and back muscles. This will also help you maintain your good posture. Push ups are a great overall exercise that don't just help with flabby arms, but also give you firm chest muscles that will make breasts appear full and less saggy.
Good posture makes your breasts appear bigger than they really are. Sit and stand up straight. Push you chest out and hold your stomach in. (Slouching only makes it seem like you have small sagging breasts).