Is it a makeover? If you can, bring a picture of your dress so they know the general colourings to work with. You should also check with the bride to see what type of look she's seeing for the bridesmaids (natural, edgy, colourful, featuring one colour, etc.).
If you have time, check out the eyeshadows beforehand (the gallery here is great for that) in case there's one colour/combination you'd really like to use. I wish I'd done that b/c the MA came up w/ two combo's and it was hard to choose, so I felt a bit pressured (she was really nice about it tho) and didn't think clearly whether I'd really like it or not.
One last suggestion: check out the bridal looks on the MAC site. I know they're for the brides, but at least you can get ideas and print a picture if you really like one of the looks.
Sorry so long, but I hope that helps!