Bras - how do they work?

I tell myself that most women wear ill-fitting bras, so I shouldn't feel too stupid about being so clueless.  Right?  

How do I know when a bra doesn't fit?!  And what can I do to make it be wearable for as long as possible?  

I've always worn bras on the loosest set of hooks, and I've had to start using the second row of hooks.. Will tightening the shoulder straps help?  I feel really stupid asking but, seriously, how do I know when I need to give up on a bra?  Where will it be loose?  Will the back strap start riding up more?  Or riding down?  

Bras are expensive so I'd rather not buy new ones until I absolutely must!

Signs of a good fit:

• No loose fabric at the top of the cups
• Straps don't slip off the shoulders
• 90% of the support comes from the band
• Nothing spills out the sides of the cup or over the top
• Band doesn't ride up in back
• No "muffin top" in sides/back
• No empty space/wrinkles at the end of the cups
• You can fit two fingers under the band on the tightest hook

Generally, I know it's time to swap when I'm on the smallest set of hooks and I can still pull it away from my ribcage. At that point, the straps are usually falling off, even when tightened all the way, and that's my go-to sign.

I have, apparently, never had a good fitting bra.  I really appreciate this list.  It's super useful.  Thank you!

I have a super-hard time with it too... straps never stay up, and I've had "tube socks" since 16!

In the past ten years, I've found ONE bra at Lane Bryant that fits, and I just keep buying it in a size smaller every time they go on sale. If I ever get below a 38 (I think that's the smallest size they make in this style) I have no idea what I'm going to do :(

I am exactly the same way with the "one Lane Bryant" bra thing :D  I have one that I love and I've gotten the same model for years and years and years.  

Your boobs should look perky in a good bra. Up near your armpits, not down near your belly button. Women need to keep their girls up high!! It's my biggest pet-peeve here. We all look SO much better in a well fitted bra, no matter what our size.

Yes!!!  A great fitting bra can make a world of difference!!!

OMG I have also never had a good fitting bra...  Always suffer from "quad boob" haha.  I have to wear a bra and a shelf bra tank to stuff myself in...  Terrible.  I go to Victoria's Secret or Cacique and try to have them fit me and nothing ever fits right.  I just wear what I have and throw a tank or sports bra on top of it to smoosh myself in haha.  Not the best practice, I know, but I'm not spending $40+ on a new bra until I'm at or quite near my goal weight.  Until then I will just closet shop for bras that are currently too small haha.  These next 6-8 months will be interesting 

I have this awesome link for when I reach my final form -- http://www.reddit.com/r/ABraThatFits/comments/rh26h/is_getti ng_fitted_for_a_bra_as_humiliating_as_it/c469bi0 -- it's full of really useful information!  

But between now and them I'm like completely lost :P

When I lost most of my weight, I went to Victoria's Secret to get fitted.  You can get fitted at Lane Bryant, Soma, or pretty much any specialty place.  The VS bras are expensive but their perfect coverage bra is great.  With a little regain, I had to get fitted again because I was popping off the top.  :( 

Kohl's has some great bras too.  Going when they are on sale and then using their coupons is a bonus.