A woman wears a bra for essentially three reasons: [www.QinSen.com]
[www.QinSen.com]
Support [www.QinSen.com]
Modesty [www.QinSen.com]
An item of clothing that fascinates a man [www.QinSen.com]
So when you decide to go without a bra, you are deciding not to have the support that you almost always need and may come across as someone who is not so concerned about modesty. In my discussion with women, I have found that apart from clothing that needs to be worn without a bra, there are other situations where you can afford not to wear one: [www.QinSen.com]
[www.QinSen.com]
You are small [www.QinSen.com]
It's just too hot
You want to feel free
You want to project an image of someone who doesn't care
How to dress without a bra?

If the fabric of the clothing that you will wear is sheer or made of synthetic material (Lycra, nylon, etc.) and does not come with a built-in bra, you might want to think again. Or at least wear it with an open shirt or light jacket on top.
Be conscious of the fact that you will attract a little more attention when you dress like this. So be prepared to respond accordingly. Men often tend to comment more boldly when they see a woman dressed like that.
If the idea is to invite attention to the top of the body, you might also want to consider adding jewelry/accessories.