OP, find someone who shares important traits with you (social & political matters, like the one you mentioned about same-sex marriage, abortion, etc) in order to avoid future & severe clashing of ideals, who is loyal, understanding and empathetic (as you will to them), and who shares or may share in the future hobbies to do with you (meaning, having something in common in regards to leisure/lifestyle).
The point is to have a happy life with this person and do things with her. That will be your life and hers, so it's essential that you're on the same vibe/page, even if that means that she does not have an exact musical taste as you (or other trivial thing).
May be hard or not, but those are the bare basics if you want a non-volatile relationship down the line.