Three agents and two editors at Killer Nashville had these pet peeves. First page especially.
Was/passives: Hard to get rid of. “Was” is like ants on a picnic.
Just: Groan. I use it too.
Proper names: Especially in dialogue.
Dialogue tags: Excess, especially if they’re not “said.”
Info dump dialogue: You can’t sneak in excess back story this way. “As, you know James…”
He shrugged, smiled, scowled, frowned, grinned, etc.: Not used in place of dialogue tags, unless they have a specific purpose. Ouch.
Lists: Yawn causing.
Vague/shifting POV: You gotta tell them who the main character is as soon as possible, and hold onto that POV.
Unnecessary dialogue: Hello, everyday stuff, etc.
Repetition: Words, actions, etc.
Telling: Know when you can tell instead of show, but it’s hard on the first page.
Backstory: We all want to include more than we need.
Setting/description: Less is more unless you’re doing literary fiction.
Grammar: Forget it especially in dialogue.
Clichés: This is the crown jewel of pet peeves.
Conflict: Even for adult writing, an agent wanted it in the first 200 words.
Typos/misspellings, stupid mistakes: Some said they would overlook an obvious typo on the SECOND page.
He paused: This was a surprise. They wanted to know exactly what the character was doing instead of saying paused.
Semicolons: Two hated them, two didn’t have an opinion, and the fifth said they could be effective under rare circumstances. I assume this was non-dialogue. Nobody likes them in dialogue.
Exclamation points: They did not mention them, but use them at your own risk.
Ellipsis: They didn’t like them on the first page or at the end of a sentence.