The best way to try to ensure it lasts -- keep looking inward whenever there's a problem, find your part in it, and learn from it. Never stop trying to do something special for the other person, even if it's something as simple as doing the dishes. Treat them with the utmost of respect, kindness, and love, and always watch closely for cues about what they want and need from you.
That said...I would also add that it is equally important to find someone who will do all of this for you in return, allowing you to have a mutually happy and supportive relationship. Don't expect that they'll get it right off the bat -- you won't either -- but make sure you both have the same kind of values for a relationship before deciding on a lifetime.