Choose your bridal outfit before choosing your style. Fussy collars or high necks look best with hair out of the way, piled on top of the head to create balance. Bare shoulders, however, work with hair down or up – although dressing hair on top of the head draws the eye upwards, creating a long line from below the neck that's elegant and especially flattering.
If your dress is elaborate, keep your hairstyle simple so you don't distract from the big story. Basically, look at what's happening with your hair and your outfit between your décolleté and your jaw line and make sure the two don't fight.
Don't forget your headdress. Whether it's a veil or a circlet of flowers, it needs to be decided upon and incorporated into whatever hairstyle you go for.