Hand Wash or Machine Wash?
To preserve the longevity of your bras, hand washing is best! This will ensure that the shape stays intact. But before you get overwhelmed by the idea of actually having to hand wash your bras all the time, keep in mind that it's super simple and you don't have to do it all that often! Simply toss your bra in your bathroom sink, fill the sink with some cold water and add some detergent. Let the bra soak for 30 mins to an hour and then rinse it out and let it air dry by laying flat on a bench or rack. Do this for each bra (cups and straps) just twice a month if you haven't been working up a sweat in your bra. You may want to do it once a week in the warmer months and air the bra out in between wears. And if you've been wearing any sort of bronzer, shimmer, lotion or fake tan on your neck and shoulders, your straps may need a rinse between wears also.
If you are going to machine wash just make sure the garment is in a lingerie bag and the machine is on a gentle or delicate cycle. Whatever you do, do NOT put your bra in the dryer. This will cause the bra to deteriorate quickly and if it has an underwire, this will surely start to poke out after some time. And you will be buying another bra a lot sooner than you expected!
Store your bras flat and stacked up against each other. Avoid folding them in half.