Designer Zac Posen, known for his dramatic, sculpted red carpet creations seen on celebs like Gwyneth Paltrow, Coco Rocha and pal, Lena Dunham, launched Truly Zac Posen, an affordable wedding line for David’s Bridal last year. At Martha Stewart’s recent Wedding Party event, the designer gave this advice on choosing the perfect dress.

“The most important thing is knowing what looks great on your body and what you feel comfortable in,” says Posen. “The only way to do that is to get in the dressing room and to start trying on shapes.”  After throwing on a variety of silhouettes he wants you to take notes, like, “that kind of neckline looks good on me, this kind of skirt bottom looks right, this is where the volume sits with me right.”

Once you found the one, your work still isn’t over. To get the dress perfect, “take the time to do fittings,” stresses the designer. “No shotgun fittings! Make sure it supports you in the right way and that’s when you’re going to have the time of your life."