Emotional: What you're really looking for here is the emotional yin to your yang. What you're not looking for is a mate who is on the same emotional page that you are. Do you really want a guy who cries every time he sees A League of Their Own? Do you want someone who becomes outraged about the same issues you do? Just imagine if you both couldn't stand bad restaurant service and both started screaming at the waiter? You'll mesh best with someone who can calm you down when you're feeling tense, and will appreciate the same from you. Now that's a good match and will come in handy when he can take care of the matters you hate even mentioning. Let's say it's time to lease a new car, and you want to start pulling your hair out just thinking about dealing with the car salespeople. Your partner, on the other hand, absolutely relishes the opportunity to shop around and get a killer deal—it's second only to sex in his book. You two could be made for each other. Just ask me how I got my last car ... my boyfriend loves wheeling and dealing over the details, I hate it—it works out perfectly.
Of course, there are many other issues in life that are more important than purchasing a new car. You'll want to pay close attention to how he handles stress, disappointment, victory, embarrassment, sadness, loneliness, joy, and myriad other emotions. He doesn't need to handle them the same way you do, you just have to be okay with the way he does handle them. Does he deal with problems head-on, or does he deny them? When troubled, does he become talkative or aloof? Which do you prefer? How do you want to be treated? Tenderly, or do you like it a little rough every now and then? Does he listen to you sympathetically, or does he race ahead to what he thinks is the solution? Do you like to be nurtured when you're sick, or do you just want him to go away and leave you alone?
Also, pay attention to how he treats his own family. Make sure he has a decent relationship with at least one family member, and bonus points if he's close to at least one sister. But beware the man who has no close relationships with any relatives. Even if they have drastically divergent standards, values, and morals, if family is important to him, you'll find some common ground. If family is not important to him, what makes you think he'll want to start a family with you?