Marry someone who loves God more than they love you.
A long courtship (dating, engagement, whatever you like to call it, I'm not suggesting anything in particular, just a long period of getting to know the person, preferably More than 12 months!) helps to ensure that there are fewer surprises, like mental health issues that could crop up later!
Decide what you are going to stand your ground on and THEN talk about the big issues... BEFORE getting married. Some of these include who & how to handle finances, # of kids, timing of kids (though God has more say in this, lets be honest), child rearing issues (broad umbrella, I know), geographically acceptable places to live (ie, what happens if that job offer comes along but it is far from everyone yall know).
Regularly schedule in Couples Time... and make it happen. Getting away from the kids, the dog, the job, the housework, the Everything and devoting a little time to talking, listening, and doing some activity together keeps the marriage going. As part of that, Date Your Spouse. By going and doing New things once a month, it actually activates the part of the brain that made those cool chemicals that your brain enjoyed when the relationship was new. The newness really is (from a brain chemical standpoint) part of the fun of the relationship. Couples who do new activities together (trying a new restaurant, taking classes to learn new skills, anything outside of their normal routine) continue to experience that newness and stay married longer.