Okay, there are like 50 different things that fall into that category, but I thought I'd start with sharing one of my most favs that was passed onto me by a great friend who has been happily married for 28 years. This one has nothing to do with the success of your marriage and future, but about living in the moment.
The wedding is next week. You've been planning this stupid amazing wedding for 12 months. You are exhausted over explaining (again) to your fiance why you don't think his college buddy should get a plus one since you've never even met the current flavor of the month. She is not worth $150, sorry. You really could do without another piece of "advice" from anyone on your hair or shoes. You are tired of making decisions that won't matter in 8 days. You love your fiance but don't like him right now, and you just want to be married already.
Now it's your wedding day. Let it all go. Remember the moment. Every moment, because you will never have it again. Even when something goes wrong, just laugh. During your reception, pull your new spouse to the side. Take 5 minutes and just look at each other, look around, soak it in. See, really see all those people around you who came her JUST for you. Because it is going to be over in the blink of an eye and you want to remember it. All that stress will totally be worth it.