Tip: You can't wear your gown to your hair trial, so do the next best thing -- pick a white or light-colored shirt with a similar neckline.
Another smart idea: Wear white to your consultation -- even a white T-shirt -- so that your hair color will be showcased atop the right hue. You should also choose a shirt with a neckline similar to your gown -- different hairstyles lend themselves to particular necklines. Once your headpiece is in place, it will make your hairstyle look different, so it's important to bring it along for the consultations. If it hasn't arrived yet, ask your bridal salon to loan you a sample. Or bring along a photo, so at least the stylist knows what to expect.
Document It
Speaking of photos, you'll want to bring a camera. Once the stylist starts manipulating your mane, ask her to photograph each finished look from four different angles -- front, back, and both sides. That way, you'll be able to see how you look from all views, and you'll get an idea of how the stylist's work translates to photographs. If there's one particular style you like, ask her to write down exactly which products and techniques were used. Since a wedding consultation can take place months before your actual event, it's important to keep notes and take pictures so you can both remember what worked.