Profiles are useful for several reasons. First, anyone who has enjoyed your book will want to find out more about you. And second, your fans will want to read other books by you. Third, profiles provide an avenue for engagement with readers.
Your profile isn't just who you are, it's who your readers think you should be.
The two foundations of a profile are:
Headshot - Readers, first and foremost, want to know what authors look like. How many times have you read a book and then hunted around on the back for a photo? Maybe, you've even done that before you read the book. Make sure your photo is professional. Depending on what you write your portrait can be serious (literary fiction), friendly (children's fiction), brooding (horror), congenial (general fiction), authoritative (non-fiction) - whatever you write, your personality should reflect your genre. A good photographer can make a work of difference, so work with a professional.
Bio - Bios are written in third person. As with the headshot, your bio should match your genre or topic. If you are writing non-fiction, your credentials are most important. What gives you the authority to write your book? If you write humor, make it clever. If you write for children, you can include your family, your pets. If you are writing general fiction for adults, write about your background, your professional career, where you live. (Do not write about your first writing project when you were in grade school!) Do you have any awards? Make sure to include them. Pretend that your publicist is writing about you - not your mother.
Where to post your profile
It goes without saying that your profile needs to be the central pillar of your website, but the two other places you absolutely must post your profile are Amazon and Goodreads. These two sites get an enormous amount of traffic. If you are self-publishing, make sure to post your profile on the platform you are using. Post a shortened profile on social media and networking platforms (Twitter, LinkedIn, Facebook, Google+). If you keep a blog (and you should), post a profile on your blog, and wherever you re-post (Medium, Scriggler, etc). Post your profile on groups you are a member of (alumni associations, professional guilds, etc). And post it where you promote your book (BookBub). In other words, post your profile everywhere you can. People who read your book will want to find you, so make it easy for them.
Helpful articles:
BookWorks has an excellent step-by-step set of instructions for making best use of your Author Central Page here: How to Optimize Your Amazon Author Central Page
You can find additional homes for your author profile here: 12 Author Profile Sites to Boost Your Discoverability
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Amazon Author Central
Amazon is the largest Internet retailer in the world, so chances are good your book is for sale on Amazon. Author Central offers a wide array of features, including bio, photos, links to your books on Amazon, videos, events, blog feed, and your own URL.
Bio - of at least 100 characters. Amazon does not support HTML in their author bios, so it needs to be straight text - no italics, bold, etc. You should periodically update your bio, but before you do make sure to make a copy and save it to your computer first. (Amazon will not save your old bio.)
Photo - between 300 and 8000 pixels in width and height. Only JPEG (or JPG), GIF, or PNG photos, no other formats. You can add up to eight images.
Blog - Amazon allows you to link your blog feed to Author Central. Anyone visiting your Author page will see extracts of your latest posts along with a link to read more.
Events - This is where you place all upcoming events, whether they are physical (e.g. book signings) or virtual. After you've created an event, it is displayed in the Scheduled Events section. People can see the venue, location, time, a short description of the event, and the book you're touring with.
Videos - You can share video interviews, book signing videos, and other videos with readers. Your videos should focus on specific features of your books or your experience as an author. You can add up to eight videos to your page. Videos should be a maximum of 10 minutes and in one of the following formats: avi, wmv, flv, mov, or mpg. Videos should be your own (not from Youtube).
Author Page URL - If you wish, you can create your own URL for your author page to post to your Facebook page and/or blogs, tweet to your followers, or add it to your email signature. A URL that includes your name is important for Google searches. When people search your name, they will be directed to your Amazon Author Central page.
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GoodReads
GoodReads is a social discovery book site with over 50 million user reviews. It is currently owned by Amazon. The site is very active, providing a venue where readers can engage freely with authors, ask questions, follow authors, sign up for giveaways. In addition to rating and reviewing books, readers can see what is on their friends' bookshelves, get recommendations, and join groups. Like all social media, GoodReads allows you to have followers. Like Amazon's Author Central, you can post an RSS feed to blog, links to your website and Twitter account.
Tips: Upload a professional photo. Make sure your face can be seen. Your photo should reflect your writing image, that is, if you write children's fiction, you should smile and look trustworthy. If you write serious literary fiction, a serious black and white photo is fine. Humor - go ahead with a quirky photo.
A solid bio consists of a paragraph or two, and should convey some interesting personal information that can’t be found elsewhere
Enable Ask the Author from your author dashboard to allow readers to contact you easily. You can’t predict when a reader might want to ask you a question, so turning this tool on gives readers the immediate ability to connect with you. Even if the person hasn’t read your book, something in your bio might spark a question.
Curate your virtual bookshelf. Readers will be curious about what kind of reader you are. Find at least 20 books to add to your bookshelf on Goodreads. You don’t need to rate them if you don’t want to. You can also create custom shelves relevant to your work, for example “Books About Maine” if your novel was set there.
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Librarything
Librarything is a community of 2,100,000 book lovers. Like GoodReads, Librarything a social cataloging website for storing and sharing book catalogs and various types of book metadata. It is used by readers, authors, and librarians. There are currently 17,554 authors on Librarything. An author profile is automatically created when you become an Author Member. Simply upload a photo, add links to your website, and write a short bio.
Then do the following:
Catalog your books. Your readers want to know what books they have in common with you. Rate and review books to let your fans know what you think.
Add your readings and other events to LibraryThing Local. Events will then show up on your author page as well, so your readers can learn about your public appearances.
Join the Hobnob with Authors group and discuss your work with interested members.
Sign up for one of their Author Chats. It's not "real-time", but takes place in one of Librarything's forums, the Author Chat group, over a two-week period. Members ask questions, and the author checks in about once a day and responds. Librarything promotes author chats by sending profile comments to every member who has listed one of the author's books.
Authors can host book giveaways on Librarything for ebooks, which is enormously helpful if you are self-published and are trying to get reviews.