1. Common ground is the best place to start.
When my husband and I were wed, we both knew so much about one another. A couple of those things, among our similiarities, were our differences. The largest one being that I was Pagan and he was a non-practicing Lutheran.
2. Be Inquisitive.
He asked me questions about my beliefs and I returned the favor. Seven years later, although our paths have grown (as I continue to study Paganism, he now pursues Gnosticism and ChristoPaganism) we are still learning new ways of uniting our core beliefs and incorporating them into our family structure. Our extended families are not something we are terribly concerned with, at the present. My family is Catholic and his family, Lutheran. I am not very connected to my family anymore. And although he is still close with his family, he has no desire to discuss his spiritual beliefs with his family.
3. Respect is earned, and that takes time.
Its so much easier to talk freely with people who give you enough respect to say what you believe without criticizing you for it. Many families do not offer individuals that respect. I know that mine did not. Remembering experiences like that, I try to be as respectful as possible towards my husband's beliefs. We both appreciate the fact that we are able to discuss our views with one another. It helps us to come together and forge a stronger foundation for our lives.