In the end, it comes down to having a good story. No amount of promo/networking can substitute.
A reminder: before you worry too much about a promo/marketing plan for your yet-to-be-published book, make sure your book is as polished as you can possibly make it. No matter what the format, how gorgeous the cover, how well-promoted….you need to have a good story and strong characters.
Take the time to hone your craft.