"Trust the reader." It's great advice. I've also heard it as "Let the reader do some of the work."
These comments and others like them come from friends and editors who read my stuff. When I self-edit, I keep the advice in mind.
It means this:
* Leave the over-description on the cutting-room floor. Let the reader do some imagining. Carefully choose imagery to imply, to create atmosphere.
* Every movement of the action doesn't have to be spelled out.
* Let the reader draw the conclusion. This goes to "showing" rather than "telling." Rather than write, "I was excited to finally meet him," write "He nodded and my heart raced."
* Omit words that add distance, such as "think/thought," "feel/felt," before saying what is thought or felt (also believed, wondered, knew, pondered--in whatever tense). Of course, there are always exceptions. If the narrative is first person, don't say "I wondered if she would faint." "I wondered" distances the main idea from the reader. "Would she faint?" might work better.
Same with third person: "She wondered if her new hairdo would make her mother faint." To show rather than tell and to avoid putting distance between the story and reader: "She took a last look in the stylist's mirror. The buzz cut offset her piercings and accented her dark eye shadow. She smiled at her mother's certain reaction--a gasp, a shriek, maybe she would faint outright."
*Avoid explaining at the end of a passage or scene what the takeaway should be. An example would be to add these words after the description of a daughter's new buzz cut: "Finally, I'd get a reaction from her." It's already clear (when she smiled) that she wanted a reaction from her mother.
Many other pointers are out there. Here's a great blog by Alan Rinzler https://alanrinzler.com/2011/06/ask-the-editor-trusting-the-reader/