If you're going for a new colour, try it out six months before the wedding so you have chance to repair or correct if it's not to your liking. Making the change ahead of time will also allow you and your partner to get used to it. You don't want to look like a stranger at your wedding!
Then have it done again within two weeks of the wedding to eliminate roots on the big day and through your honeymoon. And it might be worth adding a vegetable rinse – sometimes called a colour gloss – on top for extra shine as near to the day as possible.
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.