There is no magic formula for marketing. There are incredibly effective things you can do for free, such as talking about your book on TikTok or Instagram. It’s always best to work with a consultant or other marketing professional to help you articulate your goals for the book. There is no guaranteed result with a formulaic input and output (like spend x expect y sales). For most authors, marketing is a decades-long process of connecting with readers and getting the word out about their work. You can sign up for the conference room at your local library and do a book signing for free. You could place a full-page ad in the New Yorker for 20,000 dollars. The most important thing is to make sure you feel confident in your chosen strategy. If you are uncomfortable with social media or find it difficult to use, then don’t use it. Mailing your book to bookstores and regional newspapers with a nice handwritten note can be much more effective than constantly tweeting, especially if you don’t like doing it.