Most important (Number Zero):
Read Joe Slack's book on game design:
https://www.amazon.com/Board-Game-Designers-Guide-Process/dp/1775189201
I am not affiliated with Joe Slack. I do not receive a commission from this. But this book is an absolute must-have if you're starting out, compiling all the most important principles of board game design in one easy-to-read place.
Foreword by Jamey Staegmaier if that helps lend authority.
The short version: You probably don't want to do this.
First, your game probably isn't good and no one but friends will care about it.
Second, publishers don't generally take random pitches from unknown designers unless it's at some kind of industry event or if it's a very small publisher.
Third, self-publishing is not just a full-time job but it's an extremely financially and emotionally demanding full-time job that may or may not succeed but will definitely make you hate your life whether it does or not if you haven't calibrated your expectations properly.
The long version:
https://www.amazon.com/Board-Game-Designers-Guide-Process/dp/1775189201
Great intro to board game design. All the most important basic information in one easily-digestible place.
Absolute #1 START HERE book after which any of the other suggestions are great to follow on:
"The Board Game Designer's Guid" by Joe Slack
https://www.amazon.com/Board-Game-Designers-Guide-Process/dp/1775189201
Basically covers all the conventional wisdom that people in the industry talk about and gives you a solid baseline through pretty much every step of the process. There's a lot to read that goes beyond it but I haven't found anything else that provides such a concise foundation. In the foreword, Jamey Stegmaier basically says all that, for whatever that's worth.
Also Joe Slack is a nice guy. I've met him at Protospiel and I have friends he knows too.