Appreciating an author can be expressed in many ways. You can write them a letter or an email expressing how much you enjoyed their book and what it meant to you. Publicly posting a positive review on platforms like Amazon, Goodreads, or social media also helps spread the word about their work and can be a meaningful form of appreciation. You can also support the author by purchasing their book, attending their book launches, readings, or signing events, and recommending their work to others.