Follow SEO best practices, being careful to go with a conservative consensus (no "black hat" tactics), make sure your code is in accordance with Web Standards, and offer the best quality content you can afford to publish.
Also, take a hard look at your "good days" vs. your "bad days". If it's possible to do more of whatever is bringing people in on "good days", do that. Remember it's not all about you. Sites I work for are business sites; nobody much visits on the weekends. We probably couldn't change THAT even if we had Google's money and Elon Musk's brains....