Writing a vow is something that is super personal and not something you should seek assistance with from a friend or family member. It's something you should do alone in the comfort of a place that makes you happy in your life and in your relationship. Start with a list of all the reasons you're marrying this person. If you say they're smart, for example, write a few sentences as to how they're smart. These could be stories or moments in which they showed you that they were smart, compassionate, caring, etc. When writing these down, trust your gut and your heart.