Fiction Editor (Brigham Editorial), #RevPit Editor, YA/MG author, HS English teacher, former NBA journalist, and all-around good guy.
First, let me explain why this is problematic: We want our readers to get lost in the story, and in the first chapter especially, that happens by getting them to connect with the character entangled in their current conflict.
I've already talked extensively about the Inciting Incident, which is really the first "major" story beat you need to consider when writing your manuscript. Read the thread below for a detailed look at how those work.
The Inciting Incident is the event that pulls the character out of their comfortable world and thrusts them forward into the unknown. Something happens here that makes it impossible to keep things the way they are. It should be disruptive, exciting, and even a little scary.
Story beats are shifts in your story, and over the years, smart people have figured out where to place these shifts in your manuscript to maintain interest, meet/subvert reader expectations, pace the story, and keep your characters on their developmental arcs.
1. Read! If you haven't read widely in the genre you want to write, I suggest strongly starting there. See what excellent books look like and how experienced authors do their thing. Good writers are good readers, so if you've already read a ton, you're off to a great start!
Full disclosure: I met my agent for the first time at a @writingdaywksp conference. I pitched 2 agents at that first one, and both asked for the full. Both ended up rejecting me (including my future agent), but I pitched 3 the next year. That's the MS that got me my agent.
When you are querying a book, you are querying THAT book as a standalone. It absolutely can be the first in a series, but an agent is looking to see if they can sell this individual story. In your query, make sure Book 1 stands well on its own.
You may not have known this, but there are tools that measure a text's reading level. Mostly, they're looking at how many syllables you've got per word, and how many words you've got per sentence. The younger the reader, the simpler you want the vocabulary and syntax to be.
Before I give you a tangible word count goal for your query letter, a few words about diction: Writing MORE doesn't mean you're writing BETTER. We novelists are, by trade, wordy people, and sometimes trimming things down to their essence is the hard part.
The very first thing I'd do is check the agent's Twitter bio if they've got one. Agents with clear pronoun preferences will almost always list them there. This will keep you from using the wrong Mr./Miss/Mrs./Mx./none of the above.
Many agents will ask writers for two submission documents beyond their manuscript: a one-page or two-page synopsis (which will spoil everything), and a query letter (which will not).