Go to lots of stores to try on lots of dresses. Pack a lunch (just kidding, pb&j stains on white are hard to hide.) Make a day of it. Have fun.
Try on styles that you probably would never try. You never know.
Surround yourself with people who will be honest with you.
Buy only what makes you feel beautiful.
When you get an idea of what you are looking for, go to the cheap/poor side of town and see if the prices are better.
Try resale shops. Alot of them now have bridal gowns.For an excellent amount of cash you can pick up a gown fairly cheap. You would have to find a seamstress though.
Check the yellow pages.
Ask if there is a discount for cash.
BUT - you will have no recourse of the dress does not come in in time. So plan to use a credit card.(That way you can challenge the billing if there is a problem. Especially if you use AM Ex. )
Set in your mind just how much you are willing to spend on the dress, veil, shoes and alterations total.
I did not want to spend more than $500, actually, I was willing to go as high as $700. I spent $200 on my dress with another $50 on alterations, $20 for clearance designer Italian leather shoes (that are the only heels I can wear without suffering) and the veil was made for me.
My dress was on clearance as well. Clearance racks are my Mecca. It wasn’t poufy enough for the frou-frou crowd. And it was Ivory. I was such a rebel. ( And I originally wanted to get a light pink dress where there were ribbons on the skirt that made it look like a maypole.In honor of our wedding day, May 1st - May Day - I would have bought it, only it was only $2,500. I would have shocked all my wonderbread-inside-the-box family and friends.
It was the third dress I tried on and decided I’d take it.
This was in 1992, so with a rate of inflation, the dream dress would now be $18 million dollars…on ebay 
Oh, and get your dress drycleaned ( or preserved if you plan to pass it along) immediately. It’s 8 years since I wore mine and it’s never been cleaned and I really don’t feel like taking it in now.
Whatever money you save by cost cutting hither and yon, either blow it on the honeymoon ( I am a travel slut and beleive very strongly in travel as much as possible) or some large gift for the home. - we put a deck on our house with the $ saved from my dress and bartering services with a DJ )
Most of all, have fun!