I think one of the most important things is that they accept you for who you are. Most people would agree with this but I wonder how many truly understand what that means. There seems to be an acceptance at the initial meeting, but it ends up leading to a desire to change their partner. It's great to have support if there is a desire to change, but if there isn't, both parties just end up getting frustrated. It seems that people don't just fall in love with their partner, but the person they want them to become.
We are instructed as Christians to choose a partner that we are equally yoked with. I believe that means they must not only be in the same place (spiritually, religiously, mentally, emotionally, physically, etc.), but also the same goals and the pace that both are willing to make. Any attempt to force one to act differently, regardless how good the other feels it is better for them, will only lead to resentment of both parties.
i think that is why arranged marriages have been more successful than those based on "love." The romance we crave has also produced unrealistic expectations which have created broken homes. When I met my ex-wife, I thought that all it would take is for me to love her constantly and be the best husband I could, and she would eventually heal from injuries she suffered in her childhood. Instead, she refused to leave her comfort zone of being a victim, and instead of me raising her up, she dragged me down. The harder I tried, the more frustrated we both became. I finally had to just let her be who she wanted and refocused my life on how I felt I should serve God.