Speaking of which, I think it's always better to say "I do" than "I will." You're going to be married in the future, but you're getting married now.
But remember, it's your wedding. Anyone else's opinion about what the two of you should do or say during the ceremony is strictly advisory.
When you're told to kiss your spouse, do it like you mean it.
When you plan your wedding, try to cover all contingencies. When the one thing you forgot could go wrong does go wrong during the wedding itself, accept it and keep going. Weddings are often imperfect, like the people in them. It doesn't mean they're not still absolutely wonderful (like the people within them).
Before the ceremony, pee early and often. I know. But look, you want to be up there with a full bladder? You'll be nervous enough.
Some people don't think you should invite your exes to the wedding. But I think it's not such a bad thing to have one person in the crowd slightly depressed that they let you get away. They'll get over it at the reception. Trust me.