Make sure you both know how to compromise, especially if one or both of you never had siblings. My ex was (is) a very decent person, spectacular mother, mensa smart, topical, usually sensible etc. but she's an only child from an agnostic family...my family is huge and Catholic. The religious difference was an obvious sticky point, but the sibling thing, nobody warned me about. We ended up in grave trouble deciding, for instance, whose family to spend holidays with, and usually with me relenting to her wishes, because her parents had only one child. A great deal of passive aggression , due to our inability to argue and hash things out, soon turned into a pressure cooker as I soon found myself compliant about everything, and hadn't even realized I had lost my honor. But by that time, she was already having an affair with a surgeon at work.
Also, make sure you both know how you honestly feel about having kids and what your timeline for that might be. If you go for kids, make sure you know every detail about your respective childhoods, so you can clue in to the fact that one of you might be trying to compensate for something long ago as you're raising your own kids.
Other than that, it also helps if she isn't spectacularly hot 🙂
I have not soured on the idea of marriage though...to be closely aligned with someone in the face of life's stupid trials is totally great.
