Rule #1: Insist on emotional integrity
You gotta tell it like it is! You must insist that everything you say, imply, or insinuate is accurate, and if your partner challenges you on those messages, you must step up and own them. Mean what you say and say what you mean. You don't have to tell people everything you think or feel. But you do have to be accurate when you choose to disclose.
Suppose you're upset. When your partner senses that and asks, "Is something bothering you?" emotional integrity requires that you won't deny the message you're sending verbally or otherwise by saying, "Nothing is wrong; I'm fine." You may not be ready to discuss it, so the accurate answer might be, "I don't want to tell you right now; I'm just not ready to talk about it."
A lot of couples flagrantly violate this principle. Then they say, "We have trouble communicating." Of course they do—they both lie like dogs! And while we're on the subject: A material omission—leaving out something of crucial importance—is as much a lie as any actual misstatement.
Rule #2: Be a two-way, not a one-way, communicator
A one-way communicator talks but never listens and pays no attention to whether the listener appears to be "getting it." For her it's all about the telling, as in, "What I want you to do is go out there, get this work done, give these people this message, put those kids to bed, and come back in here." If that's how you communicate, all you know is what you've said, and you haven't got a clue about what the other person heard. Result: conflict.
But as soon as a one-way communicator asks for feedback, look what happens:
She: "Here's what I'd like you to do: A, B, C, and D. Does that sound okay to you?"
He: "Well, L, Q, R, and P don't make a whole lot of sense to me."
No wonder they're not getting along—they're not even talking about the same thing! When she checks to make sure that he has received the message, she uncovers a communication glitch. By soliciting feedback—by giving as much weight to what is heard as to what is said—you put a spotlight on the issues you, together, need to clarify.
Next: How to establish a motive