Your characters are the most important aspect of your story. This is irrefutable and no amount of debate will ever change that. Characters don't always have to be human, certainly. Sometimes, the weather can be a character (TWISTER). Sometimes an animal can be a character (BLACK BEAUTY). Sometimes an element of nature can be a character (BACKDRAFT). Most of the time, we think of characters as humans and today we're going to discuss those human characters and how they communicate with each other. After all, communication is a two-way street.
Humans communicate by using dialogue, and that dialogue goes far beyond simple speech. Even non-hearing people who speak with their hands through the use of sign language communicate beyond the shapes they create with their hands and fingers. No, dialogue encompasses the expressions we make, the body language we use, the words we choose, and the impression those movements, expressions, and words leave on those around us.
In fact, the meaning of a spoken line can come more from a body language tag than from the actual words.
Take the following examples that use exactly the same spoken words:
"You simply must come for dinner!" Marcia smiled, but it stopped dead before it even reached her cheeks. The old blow-hard would invite the devil himself for dinner if it meant saving face in front of her husband.
"You simply must come for dinner!" Marcia's bright eyes glistened in the refracted light of the setting sun, her lids squinting with the power of her smile. She touched Elizabeth's arm gently, allowing her slender fingers to linger there longer than what would be considered appropriate in civilized society.
Both of these paragraphs go to the interpretation the POV character has of the statement. Neither one may be correct. Perhaps Marcia #1 is not feeling well or perhaps she is generally insincere and this one time, she really does want Elizabeth to come for dinner, but preconceived notions of her behaviors are clouding the POV character's core beliefs.
Marcia #2 seems incredibly sincere, almost anticipatory, that Elizabeth come to dinner, but is she really inviting her to dinner, or something more?
The what-ifs are what it's all about. What if Elizabeth thinks Marcia #2 is making a pass and comes to dinner that night with all kinds of mischief on her mind, only to discover that Marcia #2 wants to sell her an Amway membership?
What if Marcia #1 isn't really a blow-hard, but a battered wife who must weigh and measure every word, every instance of expression or body language, and every impression that she leaves with others to avoid a beating from a jealous and controlling husband?
Commit this to memory and use it every single time your characters speak to you or to your reader: It's not just what our characters say, nor is it how our characters say it. It is also about how our characters interpret what others say and do and how that affects their overall core belief system.