How do you balance action and dialogue in a scene without losing the reader's attention?

The dialogue weaves meaning into the action that's going down, and the action should take place within intervals of informative dialogue in most cases. Sometimes the action and the scene are simple, but other times the dialogue defines the events that surround the characters in very meaningful ways. Dialogue can reveal next moves or foreshadow next actions in the exhilarating short window of time within which your events will unfold. Our characters voices are shaped by the events surrounding them... but at the same time we shape their voices to accord with the upcoming sequence of events. It's a very interesting interplay where you get full control.

When developing a main character you give them traits and attributes such as their physical condition, age, intelligence, style of dress, social class, etc. If you give them their own, unique voice, their distinct way of speaking--one you can actually hear as you write about them--it helps you more easily show their overall character. It also helps in the creation of scenes with dialogue because the main character's voice is already established for the reader, and is the pivot point which other voices must react to.

I agree - keep dialogues varied in all ways. I think immediately of Charlie Mackesy's wonderful book: 'The Boy, the mole, the fox and the Horse' What a most beautiful example of rich, descriptive dialogue opening up a beautiful adventure of four very different characters. See how each dialogue lends to the action and story opening up. Experience the themes coming through and the beauty of language enriching a story. The effect of a metaphor, for example, lifts the dialogue, when the Horse says about kindness: "It sits quietly beyond all things." (citation from 'The Boy, the mole, the fox and the Horse' Penguin Publisher 2019 - by Charlie Mackesy) This book uses such effective dialogue, it is a true pleasure to read and learn so much from.

Unless the scene is a one-time encounter, don't have the characters reveal everything they know or feel. Use the scene as a building block that moves the story ahead. Save some of the emotion and information for another scene.

God took me to the step I needed to follow when He called me to be a writer. I was not a reader or writer most of my life, but God had plans through His Son that were not revealed to me until my fifty-second year. I was not an Author or writer until their gifts came to me like a cool wind on a hot summer's day. Any true writer has a particular style of writing that reflects their voice and the scene through words they want to express. They will become their editors and sharpen their articles, stories, and books as much as their gift allows. Editors called to be editors can still sharpen an Author's gift through their gift to edify the Author's words more profoundly.

Additional ways to see if the dialogue has a natural feel and is working the way you hope for: read it out loud to someone else, and have it read out loud to you. Reading a scene to yourself is important, but reading it to someone and hearing someone else read it may reveal strength or weakness in the scene.