The Big Picture:
Do you have a favorite dress? No, not a wedding dress in a magazine, I mean a favorite you own. That dress you always grab when it is a 'dress day'. What do you like about it? Is it the way the color flatters you? Or how the fit and fabric feel? Or the way it enhances your assets? That thing you love about your favorite dress should be the starting point when looking for your wedding dress. Dresses aren't your thing? Explore other options; there are no hard rules. You want to be comfortable, look beautiful, and still be you.
Remember this is a thing you will wear all day: inside, outside, standing, sitting, dancing, kissing. If you are buying a dress new 'off the rack' try moving in it. Make sure you can sit if you are tired and get low if you are dancing up a storm.
I know it sounds obvious but think logically about when and where your wedding will be. If you are having a mid-summer beach wedding a long sleeved corset ballgown might be less then ideal. If you are having a winter wedding a short skirt might be a challenge. You can make anything you want to work, you just don't want it to be to much work.
Final general note: This is a dress not a car. No matter how much money you have, and how beautiful the dress is, it is a one off purchase. Chances are slim that you will ever where it again, so there is no reason to blow 25% or even 10% of your wedding budget on it. There are plenty of beautiful dresses in all sorts of price ranges, new, used, or otherwise.
Beautiful unique dresses at prices compairable to more genaric stores like Davids Bridal
All sorts of preowned options, with a wonderful 'dress altert' feature if you are looking for something specific.
Again a great resource for not quite new dresses.
I went to a lovely boutique and tried on some stunning dresses, all of which were about as expensive as our entire wedding. They were works of art. And I couldn't sit or dance in most of them. That to me is just silly. Luckily I have amazing friends who are so talented and are making my dress as a wedding present. I cried I was so honored. But not everyone is so lucky to be able to curate the dress of there dreams, made with love, and I know that. But I also know that those wonderful ladies and my self are broke recent university graduates. This dress will not be made from the finest silks of the world, diamond encrusted, and pearl beaded. I'm about to start an unnecessary tangent about consumerism... Stoping before I start. My point is take the resources you have and find a way to have the dress you want.