Hi, Mellllls.
Strangely (considering that I'm not married), I have loads of experience with this. I worked in bridal for many years when I was younger, in design, production and retail. One of my first jobs in the fashion industry was working as a design intern for Justina McCaffrey (you might not have heard of her- she's like the Vera Wang of Canada ;), and I ended up managing her flagship boutique for a short time, too. I have helped *loads* of women pick out their wedding dresses.
So, here are my top tips:
1. If you can possibly bring yourself to, go shopping alone, or with just one or two other people (you MOH, mother). It is so much easier to pay attention to what flatters you/what you really like without a whole bunch of opinions flying around. Once you have a better idea of what you like, or even a few "finalists" picked out, you can go back with a larger contingent (it often takes several visits to the same salon to buy a dress!). I know wedding dress shopping seems like a fun thing to do with a big group, but the brides who show up with all their bridesmaids, mother, mother-in-law, etc. tend to have a harder time making a decision, and (in my experience) are more likely to doubt it later on.
2. Definitely try on loads of different styles/shapes! This is so, so important. There were so many times when I had women come in and say "I want x, with y sleeves, in z colour" and ended up with something completely different, which they loved! We don't often wear gowns these days, so it's hard to tell what will actually flatter you until you start trying them on. To that point, I agree with Julie- let the assistants pick some things out for you, because they'll likely have a good eye for it.
3. Having said that, don't be afraid to tell a pushy assistant NO. If you know that you don't want a ballgown-style skirt, don't let someone bring you one after another (maybe just one, to make sure that you really don't like it).
4. Wear a good strapless/convertible bra (even if you don't want a strapless gown, it will be the least likely to interfere with the dresses) and nice, new panties! Sometimes the assistants will end up seeing you in them, if a particular gown is tough to get into, or is a sample size and needs to be held at the back. (Don't worry about it- they do this every day!)
Hmm, I think that's it for now. I will keep thinking though, and get back to you if I come up with any more. Hope you have a great time!