Marry someone you love, make an effort to be happy, dont argue about stupid shit, quit being a prick, dont marry a cold bitch, dont be a jackass, do something nice every day
My answer is that you have to cultivate some mindfulness of the importance of your marriage. In a way, Bressus' post, which I quoted describes some of the practical actions this would entail.
Most people have a lot of bad mental habits and their attention wanders. There's a lot of little competing voices that bounce between what happened in the past and what's going to happen or what we want to happen, with little attention paid to the present. Anyone who has engaged in any sort of meditation practice will likely know where I'm going with this. When something catches our interest for a while, like a workout routine... or another person who we fall in love with, we are for at least a while drawn into the present. But mental weakness often sets in over time and when the relationship is no longer novel, instead of thinking of our partner and how we can be happy by making them happy, we let our mind wander and we begin to think too much about work, or maybe some new skirt at the company we work (or new guy), etc. This is often the broad pattern of why couples who otherwise do care about each other fall into patterns of neglect.
The solution then is simply to bring your attention back to the relationship. Cultivate mindfulness and appreciation for the person you married. Most people are giving and want to do things to make their significant other happy before marriage and in the early stages of marriage. And I think most people remember that the act of giving alone made them happy. If you learn to do that again (without expectation of something in return!!!) then you will become happier in turn by seeing them happy. When that happens, warmth and attraction... and sex... tend to follow.
I guess if the other person is too far gone themselves to appreciate your efforts, it won't work, but I would suspect if one partner makes the effort and is patient, they can often reach the heart of the person they love and things will improve. Of course, mindfulness is a life long effort. To some, it will seem hard, but I would think the rewards of a loving relationship far outweigh the work involved in keeping a relationship from falling into neglect and discontent. And if my answer seems blah, just understand it's an explanation of the process behind Breesus' post-- at least as I see it. You don't have to get all into meditation and things you find hokey... you just have to be there for the other person and make some effort to make them happy.