1. Send her a love letter.
Let's assume she's jittery the morning of the wedding. (Not the am-I-making-a-mistake kind but the OMG-I'm-really-getting-married-to-my-best-friend variety.) Have one of the groomsmen deliver her a sweet and simple note from you while she's hanging with her girls and getting ready a few hours before the wedding. Nothing soothes a woman's nerves more than a declaration of love from her man.
2. Confirm the best man has the rings.
One of the few actual chores (lucky you!) on the groom's to-do list involves making sure the wedding rings make it to the ceremony on time via the best man. You know the guy better than anyone else—is he the responsible type or a flake? If his head is in the clouds most of the time, remind him to put the rings in the wedding jacket or pants he'll be wearing that day. Sure, if he forgets them back at the hotel, no one's going to shout, "Stop the ceremony!" but borrowing two rings from guests and pretending they're yours is kind of lame.
3. Eat smart.
Look, dude, we aren't worried you'll forget to eat and drink on your wedding day, but we want to give you a heads up on your choices. Raw onions, tuna fish, garlic, and strong coffee are way too odoriferous for someone who's going to be kissing and hugging dozens of people all day. You want people to remember how handsome and charming you were, not how badly you needed a breath mint.
4. Play Xbox.
Or watch a football game, go for a run, play a round of golf—the point is to do whatever relaxes you. Everyone considers the wedding the bride's day but, of course, it's yours too, and your nerves might also be on edge thinking of the life-changing event that's about to happen. Be your most happy, relaxed self later by doing something fun beforehand.
5. Practice your wedding vows out loud.
You took the time to write personal vows, so you'll want to deliver them to the crowd with passion and exuberance. Since that kind of thing takes practice, it's worth spending 10 minutes repeating them out loud (looking at yourself in the mirror: optional) so they'll feel comfortable and glide off your tongue rather than trip and fall like a verbal Jennifer Lawrence at the Oscars.
6. Show up on time.
If anyone gets to be fashionably late for the ceremony, it's the bride—dealing with the dress, the hair, and the weeping Mom takes time, you know. But you, the guy who's basically wearing a fancier version of his everyday outfit of pants and shirt, should be ready in minutes (we'll give you an extra five if you're putting on a tie). So be prompt and get the party started!