KNOW YOUR CHARACTERS
Readers want strong characters, sometimes a character they can relate to. You need to have your characters ready in your mind. If you want to change their personalities more later on, you can do that, there is nothing wrong with that. Just know the basics for a character.
What if their personality; Snarky? Sarcastic? Shy? Angry?
What is their goal by the end of the novel? Is this a series, what will happen to the character by the end of the series? Will they overcome obstacles?
All of these are important facts when creating your characters. If you know your characters inside out, you can get that story down faster. While you're writing keep your character map next to you, so you can keep their personalities going. Remember your characters are the key to your book.