How do you balance the use of vivid imagery with pacing to keep readers engaged without overwhelming them?

In the context of fiction writing, one area in which this balance is found (largely anyway—for me) is through zooming in and zooming out / exposition and action. If you have a large section that is zoomed way in on a character's POV, where we're getting a lot of sensory information—action, close in—then you might want to consider following with a brief period of zooming out, broad strokes, covering large swathes of story/history, giving context for a period. This can also be seen as balancing action with exposition—it's not all about showing and not telling. Telling is equally important.