Ready for some clichés about marriage? Here they come. Because they're true.
Marry someone with similar tastes and preferences. Which tastes and preferences? The ones that will affect life almost every day.
It is OK if you like the ballet and your spouse doesn't. Reasonable people can accommodate each other on such differences. But if you dislike each other's friends, or don't get each other's senses of humor or—especially—if you have different ethical impulses, break it off and find someone else....
It is absolutely crucial that you really, really like your spouse. You hear it all the time from people who are in great marriages: "I'm married to my best friend." They are being literal. A good working definition of "soul mate" is "your closest friend, to whom you are also sexually attracted."
...A good marriage is the best thing that can ever happen to you. Above all else, realize that this cliché is true. The downside risks of marrying—and they are real—are nothing compared with what you will gain from a good one.