1. Marriage is a commitment to hard work. You won't know really understand this until you're in the middle of the worst of it.
2. Sometimes you won't like your spouse; that's ok. Tomorrow is a new day.
3. It's a partnership; you'll bring something new and necessary to the mix, and you'll also be a difficult partner in some ways (sex, money, your family, your need to have 14 chihuahuas...)
4. You'll never completely know the person you're marrying, so stay curious and don't assume.
5. It's easy to find out who you are while being single; the real challenge is learning who you are while living with another person--kind of like learning to juggle while jumping on a trampoline. (see #1)