For more significant guidance, additional detail, or just because there's a lot more in the book than the idea of micro-tension, you'll want to get your hands on a copy of Fire in Fiction by Donald Maass. The chapter I'm working from is Chapter Eight, Tension All the Time.
Maass has the amazing ability (honed from years and years of studying writing) to pick up a sample and tweak it to add undeniable tension. Or intrigue. At the workshop I attended, a brave soul offered up her YA manuscript with a bit of dialogue to see how it could be enhanced.
Her scene had two people waiting for a bus. An older woman and a teen girl with an attitude. What Maass did to make it better was to get to the goals and emotions of the individual characters. The older woman was nosey, and the younger girl wanted to be left alone. Super conflict for tension in the dialogue. His immersion into the psyche of each character ratcheted the words each one uttered. Amazing.
From Fire: Tension in dialogue is emotional, not intellectual. It comes from people, not topics.
Writers will sometimes feel we have to risk backstory and info dumps to help the reader understand the situation, and in some cases, we're probably right. But there's no way we can turn information into riveting writing. It is what it is. Sometimes we can make things a little better using dialogue. But it must be infused with tension. One of your characters has to have an opposing goal, or a disbelieving view, or something that makes the dialogue relevant and interesting.
And don't forget inner conflict. That can be expressed in dialogue as well. Do they indicate that what they're about to say is really none of their business, or something else even more dramatic?
Maass gives an example of creating tension when the dialogue is between friends. Then, the writer must rely on friendly disagreement. But there is still an element of strain. Does the character think they're friend is making a horrible decision? Do they refuse to back down?
From Fire: Where is the tension in your dialogue? Is it present in every line? Why not undertake a dialogue draft? Check every conversation in your story. Are you relying on the circumstances or the topic itself to make it important for us to listen in?
That is dangerous. Instead, find the emotional friction between the speakers. Or externalize your characters' inner conflicts. Or pit allies against each other. True tension in dialogue comes not from what is being said, but from inside those who are saying it.
Maass says earlier in the chapter: Micro-tension is easily understood but hard to do. I know this because when teaching it in workshops I watch participants nod in understanding when I explain it, but see them stare helplessly at their pages when they try to do it themselves.
Was I that obvious?
CR: Identity Crisis by Debbi Mack
It's all better with friends.