A prenuptial agreement is one that you enter into before you get married. It is meant to protect both spouses in the event the marriage doesn't work out. All of the terms of the agreement need to take both parties into consideration because it can't favor one person over the other. It is possible for the court to throw a prenup out if it does overly favor one person.
When you are getting the prenup terms hashed out, make sure that you have a your own counsel. You can't use the same one because there is a conflict of interest in doing that. Even though you and your future spouse are working as a team on the wedding and your future, this is one area where there has to be a division.
You can't include things in the prenuptial agreement if they are off limits. One example of this is child custody and support. Because you have no idea what will be in the best interests of the child at the time of a divorce, you can't include those terms in the prenup. Interestingly, you can include information and terms regarding alimony in the prenup.
Additionally, make sure that you are protecting assets that you have going into the marriage and ones that you might inherit during the course of the union. You don't want to lose a family heirloom or home because it wasn't covered in the prenuptial agreement. Even though these things are usually considered separate property, there is a chance that they might "comingle" with marital assets.
Each prenuptial agreement has to take the specific circumstances of the upcoming marriage into account. Be sure you start this process long before the wedding, so you have time to determine how to handle everything.