Key differences between men and women that are at the heart of most relationship issues.
For instance, if your boyfriend or husband is hardly ever home, rather than saying "why aren't you ever home?" say "I really love it when you're here." If your partner isn't meeting your needs, it is always a much better strategy to tell him what you want rather than constantly affirming what it is you don't want and pointing out the ways in which he's failing to meet your needs.
Remember, he wants to make you happy and the more appreciated he feels, the more he will go out of his way to give you what you want.
It is also worth noting that men respond to specific compliments much more than abstract ones, for instance, saying something like, "Thank you for doing the dishes, that was so thoughtful of you" packs more punch than something general like "You're so thoughtful." This can be an area of confusion since women are thrilled with general compliments (You're so smart/pretty/nice/funny etc.). (MORE: 5 Things Every Girl Needs to Know About Guys)
While the principles I've outlined may seem fairly straightforward and universally understood, they often get completely ignored. The biggest mistake most women make in relationships is assuming men think just like they do. It is only when we embrace our differences and see the other side more clearly that healthy communication can flourish. Try it out for yourselves and you'll see what I mean!