How to Determine What's Important and What Isn't When It Comes to Personal Differences?
Ah, difference. It is the spice of life for so many people. Who wants to eat the same thing day after day, or see the same four walls all the time? And who wants a friend who agrees with everything we say, whatever we say, only to make us feel like we are living in an echo chamber? Yet on the other hand, too much difference can lead to constant conflict, constant flux to the point of chaos. Whether we are talking about foods (because sometimes we really do want to eat the same thing twice in a row!) or friends (who should at least tell us we are right some of the time!) -- some amount of similarity is important.
As with everything, this issue is about balance. When it comes to choosing a partner, it is an especially important balance to maintain, because this will be the person with whom you will be spending your life, making the decisions that effect not just you, but your children as well. And unfortunately, this is an area that too many people spend too little time understanding, not only about their future partners, but about themselves.

And this is where you have to start: with yourself. You need to know yourself, to know what is so important to you, in your core, in your gut, that you cannot compromise. You also need to know what kinds of things you are able to let go, what differences are of such minimal substance that you don't care what other people think about them. This can be a hard line of thinking and feeling because there is a wide world of subjects, ideas, and such to consider; it can help to break things down into categories.
Culture is a good thing to start with. It includes traditions, religious as well as secular, food and clothing choices, roles that men and women take when married, and so forth. Are you the kind of person whose faith is important to her? Then you need to ensure that your husband shares your faith; this is an area in which a personal difference would be a problem. Same with food; is it of critical import that you share meals with your family, no matter what? Then it is very possible that a traveling salesman is not the best choice for you.
It can help to make a list of such critical things, again starting with culture. Write on one side the issues and areas about which you cannot compromise, and on the other, include the things that you can easily let go of. For example, if you truly don't care about the religion in which your children are raised, then you can include it in the column of issues for which personal differences are no trouble at all.
Once you have exhausted culture, move on to things like politics (do you care if your husband is more liberal or conservative than you are?), friendships (is he incredibly social, while you are an introverted person?), and such. Try to think of all of the areas of your life in which conflict has arisen, think about what brought about that conflict, and include those issues on your list. When you are done, sit back and read what you have written!
If everything you have on that piece of paper is in the "no-compromise" column, then you probably need to think about loosening up a bit; no one will agree with you about everything! On the other hand, if it appears that you don't care deeply enough about anything to not be willing to compromise, think a little harder -- surely something is that important to you! It isn't that you can take this list with you to see how your potential husband will rate; but you can and should keep it in mind when you are on dates.