Go through the process of writing and proofreading

Close the door and write alone.
Write the first version of the book alone, in the isolated writing room, and do not show the manuscript to anyone.

Read your book after at least six weeks.
When you finish writing, leave the manuscript for a while before you read it. Don’t read it for at least six weeks. After six weeks, read it and start correcting all the mistakes you see. Pay attention to logical errors: Do your characters have good behavior motives? Are all parts of your story connected to the book’s central theme? Delete unnecessary words, sentences, paragraphs, and everything unrelated to the book's main point.

Get feedback.
Give the book to friends or family members to read. They will point you to some things you may need to correct, such as the speed of the story plot development.