Determine to stay committed to your vows and covenant (marriage is a covenant, you know!).
True commitment yields not only a better marriage, but, when times are difficult, it tends to force partners to actually resolve conflicts (better to resolve than live unhappily ever after) by compromise, Biblical instruction, self-examination, etc.

Meet your spouse's needs
His Needs, Her Needs and Men Are From Mars, Women Are From Venus are two excellent (and recommended) books that expose the myth (if ever there was one) that men and women are the same. And since we are different, we must deal with the opposite sex as -- well, opposite or at least different from ourselves!

Become and stay friends
Fully developed marriages maintain the friendships begun in courtship by keeping up on one another's interests and participating together in them as much as possible. Truly happy marriages are first of all friendships.

Let God's design for marraige prevail
Modern social experiments spearheaded by sincere but mistaken people to improve on God's original model are at the root of much marital conflict (also familial conflict). God's design makes no one a doormat (contrary to "progressive" accusations).

Learn the art of conflict resolution
The earliest conflict resolution we become acquainted with (and sometimes the only) is win/lose. But it needn't always turn out that way. Compromise and occasional win/win solutions can be obtained through reasonable communication and a little "thinking outside the win/lose box".

Hold the same values
Marriages brought together by sexual attraction often find themselves in conflict about their most closely held values. Values are the foundational ideas that each person holds about priorities, conscience, religion, truth, principles, scruples, codes of conduct, philosophies, rites, outlooks, and culture. Of these, religion is the most crucial, because one's religious faith will inform most of the other values in part or in whole. Thus, marriages with different religions is often conflicted (exception: when the real religion of both is "apathy").

The knowledge that love can be revived
Successful marriages understand that love is a product of how I treat the other person. It isn't a product of mysterious, magical, magnetc forces. So successful marriages never completely stop dating. And when busyness makes love wane, successful marriages mutually work at it rather than romantically (or perhaps lazily) assume that the magic is just vaporized.