I recently read a post by Nathan Bransford. He was commenting on spicing up dialogue and made a point that everyday dialogue is boring. I partially agree. But, I think that, as with many "rules" in writing, this situational advice cannot be applied with a broad stroke.
Our goal as writers is to willfully suspend disbelief. Dialogue is difficult. It must convey tone, mood, and character, move plot, provide action and back story, and most of all be believable. To spice up dialogue to make it more appealing is a slippery slope. My point is that ordinary dialogue or dialogue that is about everyday life, is very boring. Choosing toothpaste, asking your children to take out trash, mundane discussions about clothing, politics, and such do not make for riveting dialogue. They do not provide action, or move plot. With this much I can agree.
However, dialogue that is too well planned out, too stilted, too exact can lead a reader to see through the thin veil of fiction. Often, every character is suffused with the intelligence, cadence and voice of the author. No differentiation between characters exist. This can be dangerous. It does not provide the reader with palpable differences between characters. They all become similar because they all talk the same. And if their dialogue isn't different than the narration, then the slippery slope becomes even steeper.
Try this experiment. As writers, we are supposed to be good observers and cataloguers of human nature. For one day, try sitting in crowded rooms or busy places like parks. Listen to conversations. Don't eavesdrop, per se, but allow yourself to listen to the different voices, the different deliveries, and intensities. We are limited in writing sometimes--often we can only get across auditory tones by way of descriptions of the conversation delivery. But, note the content. Note how different deliveries of speech color the message. A nasal delivery drones, a deep voice booms, a gravelly voice sounds testy, a soft voice sounds melodic. Use those cues.
In this experiment, you can also note what content is mundane and what may qualify as "spicy" dialogue. This exercise is a great writing prompt. Try using this experience from time to time to write a scene from a novel, a short story or just a journal entry. It is a wonderful way to practice dialogue cadence, to learn how to convey the natural rhythm of speech in your writing.
It is important to understand how people talk. It is also important to know when to edit those conversations for the sake of the novel. Spicing up can mean cutting out dialogue that doesn't fill one of the duties of dialogue I listed earlier. Spicing up dialogue can also mean adding elements of conversation that make a conversation seem real and connected to the characters that are speaking. What your characters say can make them come alive as much as what they do.