It seems one of the most common things that happens after the altar is that couples that were previously completely invested in each other start to grow comfortable, which is often just code for complacent. They often unintentionally neglect the very thing they value most - their marriage.
Dr. Harley contends that couples that want to save, or even improve, their marriage must spend time together. That seems straightforward, I know, but apparently couples report being way too busy to enjoy their spouse's company! In his work with couples, he puts forth his strategy in The Policy of Undivided Attention. You're probably too busy to read about it, so I'll recap it here:
Basically, marriages improve and often thrive when both individuals are committed to spending time together. Dr. Harley recommends 15 hours per week of alone time together. He recommends that the 15 hours should be protected - undivided attention (mutually facing a movie screen doesn't count!) - away from kids and often away from the home. And for best results, it's better to spread the 15 hours throughout the week. He suggests that this is the only way to really sustain the love, and there's nothing shameful about getting out the calendar to make sure you fit it in. If you're not sure what to do, just remember back to how you acted when you were dating. Do that.