There really isn't advice to give after someone has gotten engaged. I recommend everyone live together and have sex before marriage. I also recommend people talk about life, parenting, and financial goals. For example, if the couple has differing views on religion, you should know the compromises by now on things like circumcision, baptism, going or not going to church, etc. What's there view on spanking? Do they know whether or not they even want kids?

Since they're already getting married I would say to try to step back every now and then to judge a situation. Try to be more self aware. If you're lacking in affection or responsibility, then acknowledge it and try to adjust. I recommend kissing each other every night and saying I love you. Even if you had a fight and don't want to kiss, at least say I love you..even if you mumble it. Don't say anything you can't take back, especially comments about divorce. Don't bring up the score of what you brought to the table. If there's a pay gap between the two of them, that doesn't matter..it's shared money now. Don't keep track of who bought more furniture or paid more for groceries or who is actually making the mortgage and/or car payment. You're a team now.