Couples have problems which make them slowly grow apart. If I were giving you only one relationship tip I would say, don't lose the intimacy. No matter what happens keep the intimacy alive. Touch is one of the fundamental things people need to feel close to each other.
Affection is key; a hug, a kiss, holding hands can be more effective and powerful than you think. The level of a hormone called Oxytocin your body produces increases with affectionate touch.
Touch is vital to a healthy relationship. It helps to brings the walls down just enough to open up the lines of communication.