If you are still writing your first book, you should call yourself a "writer." If you have published your book, call yourself an "author." Tell everyone you talk to what you do when they ask ("I'm a writer/author") and tell them about your book. Spread the word!
Use social media that you are already using to post about your writing process and ask for advice or opinions, or post excerpts from your book. The Six-Word Lessons books are perfect for short tweets with a brief description and a link to the book.
Patty Pacelli, author, editor and publisher, writes hints and tips for authors and writers about self-publishing, writing and marketing your book.