The first things they’ll probably ask you are what kind of styles you like and what your budget is–the reason is because they probably stock LOTS of styles and in a variety of price points. They don’t want you to fall in love with a $8k dress if your budget is $2k, you know? And, if you know you like something deconstructed and sleek, there’s no use in trying on poofy ballgowns with lots of boning. So it’s good to think about this before hand.
I suggest that you bring spanx–my consultant helped me in and out of every dress and I felt far more comfortable with the spanx on… we got VERY close–ha ha! I did not bring a strapless, and they provided several try-ons in case I needed them (that were nice and new-looking, I didn’t feel weird trying on dresses with these).
I brought my sis the first time and then returned the second time (after "sleeping on it"–that is very good advice) with another friend. I would say bring someone who knows you really well and is comfortable being totally honest with you. And when you find a dress that you really love–try on the veil! I never thought I would want a veil, and I tried on a cathedral length (go big or go home!) with my dress, and it just about brought tears to my eyes. Needless to say, it made me love the dress even more and it was a really special moment.
You should know that it may be a little different than other shopping trips, where you just causally shop until you’ve made your decision… since they have appointments (and there may be one after you), you may not have all the time you would like (depending on the salon)… so I suggest that you try to select the dresses to try on as quickly as possible and then when you put on a dress you know is not you, don’t hang out in it too long (I did this with my first dress… I totally didn’t like it on me, but it was the first "wedding dress" I had ever tried on, so I wanted to really take it in… and I did, but then by the end of my appointment, I felt a little rushed). With that said, it’s not like they’re going to be rushing you around (unless they’re bad salespeople!)… so I guess my advice is that you should just be conscious of time so that you don’t find yourself wishing that you had more (and thus, needing to make another appointment for a different date).
I also suggest bringing some fancy shoes, something from your closet. You don’t need these, but sometimes when you put on a dress that you really like, having shoes that you like help you to visualize the entire look.
Have fun! I ended up buying the second dress I tried on, during my first shopping trip (and have not and will not go shopping again!), so part of me wishes I had the opportunity to do more of it!