It should look good!
Always try your bras on wearing a t-shirt – it's the best way to see what it's doing for you. A great fitting bra can make you look taller, will define your waist, and even make you look slimmer!

Don't settle for wrinkles
If you see extra fabric or wrinkly, baggy cups, the cup size is too big. Try sizing down.

Don't fall out
Take a look at the front of the bra. There shouldn't be any breast tissue spillage, puddling, or falling out of the bottom of the cups. If there is, your cup size is too small. Try sizing up for a flattering, more natural looking fit.

Straps shouldn't work too hard
Your bra's support comes from the band, not the straps. So be sure that you're wearing the correct band size. Too big, and your straps will end up taking the weight, which will cause them to put pressure on your shoulders and dig in.

Is your band straight?
Look in the mirror from the side. Your band should be at the same level all the way around. If it is riding up in back, it's probably too big. Try sizing down a band size or tightening your band.

Mind the gap
The center front of your bra should lie flat against the breastbone. It should not lie on top of any breast tissue. If there's a large gap, you may need to go up a cup size.

How tight is right?
Your band should feel firm and secure, but you should also be able to slip two fingers beneath the band in back, and one in the center in front. If you can't, you may need to loosen your band a bit, or go up a size.

Underwires shouldn't dig
Underwires should lie flat at the front of your bra, against your ribcage. If you feel your underwire digging into any breast tissue, you should try a larger cup size or a different style.

Bras stretch over time
When you first wear your new bra, you will wear it on the loosest hook to get accustomed to the way it should fit.  However over the first couple of months you will move it to the middle hook because of the wear of the bra and over time you will move it to the last hook because it will stretch.  A bra from start to finish should last about 6 months. 

Place yourself in your bra
Now that you've found your size, test your fit. Take the opposite hand from the side you are adjusting and gently bring the breast tissue from the back to the front. This movement will help you settle your breasts correctly into the cups.

How to know when you've found a perfect fit?
Your breasts will feel like they are "sitting" in the cups, you will not feel any underwire pinching and your bra will feel comfortable and supportive. You shouldn't have to settle for a so-so fit. Sometimes you will have to go up a cup size or two. Don't let it concern you – sizes do vary among brands.

Reminder
Check back in six months or so. You should re-evaluate your bras regularly to be sure they are fitting you the way they should – because a woman's body does change over time, usually 6 times over the course of our lifetime.  Bras stretch and lose shape with repeated wear and washing. It may be time to stock-up again, soon!