I ordered my dress in February 2013 and got married May 2014. It took about 7 months for my dress to come in. I loved my dress and had no regrets. Just don't make any rush decisions.
I ordered my gown 18 months in advance. I Love it and knew I wasn't going to change mind. It takes 6-8 months for it to come in also. In the words of the owner of the bridal shop I went to...it is never too early!
Even though I didn't go through a traditional dress shop (yay Ebay), I ordered my dress a year before my wedding. I'm not one who changes their mind easily, and I was honestly more concerned with finding the perfect shoes so wanted to have plenty of time to find them before having to get fitted.
If you buy your dress early, more then eight months out make sure you love that dress because with all the choices out there you could feel you made a wrong choice.
Unless you buy off the rack or at David's Bridal, many dresses can take around 8 moinths to come in. Allow time to find a dress and for alterations and I'd say one year is good to start your search.
Oh, and one thing to note, once you do find your dress, stop looking at others! That's how many get buyer's remorse.
Re: Question regarding Wedding Dress shopping?