Decide who has the rings before everyone walks down the aisle.
Bring your marriage license if your state requires it at the ceremony.
Tell your officiant how to pronounce every name they'll say out loud.
Decide exactly how you want to be introduced.
Print or bring a backup copy of your vows.
Ask someone other than you to be responsible for important ceremony items.
Have a weather plan for an outdoor ceremony.
Leave a little room in the schedule. Weddings run late.
Tell your officiant where to go when they arrive and where they can park.
Actually look at each other during the ceremony. Your guests will survive without your attention for 20 minutes.