People will wonder this for years, and I think every successful relationship shares some similarities but also has it's own unique reason it just works. However, I think it's good to continually learn and try new things! A researcher poured through about 50 years worth of studies on long-term relationships.  And he thinks he found the four key things you need to do if you want your relationship to last. 

1.  Stop thinking you can do better.  A lot of couples break up because one person decides they could UPGRADE if they wanted to.  But then they usually realize they're older than they used to be, and dating is harder than they remember.

2.  Decide your relationship is more important than your individual needs.  In other words, you're together because you truly believe you're stronger as a whole.  And you're not just with them because they're attractive or make more money.

3.  Don't let conflicts fester.  When you fight or disagree on something, talk it out.  Because if you just ignore it, you'll resent each other.  And don't just try to win every argument.  Try to resolve them, so you BOTH feel better by the end. 

4.  Make each other laugh as much as possible.  It's even more important when things get really stressful.  If you can make each other laugh and RELIEVE some of that stress, you can end up connecting on an even deeper level.  (Inc)