To become an online book proofreader, firstly, you need to cultivate a strong command of the English language, including grammar, punctuation, spelling, and vocabulary. Then familiarize yourself with the common writing styles, such as AP Stylebook or the Chicago Manual of Style, because these are crucial for proofreading. Moreover, participate in online courses, workshops, or degree programs to gain hands-on experience. Also, online book proofreaders have a digital presence as well. So to get work, you can set up your profile on platforms like Upwork or Fiverr to connect with clients and find proofreading gigs.