Everything below I learned from Yoast. I’m just offering my adaptation, which includes nothing original.
1. Make sure that your posts link back to your author archive page. WordPress automatically includes a rel=”author” tag in this link.
2. Add the following code to your functions.php file to prevent WordPress from stripping rel tags from your author bio:
$allowedtags[‘a’][‘rel’] = array ();
add_action( ‘wp_loaded’, ‘allow_rel’ );
3. Go to your WordPress profile (YOURDOMAIN.com/wp-admin/profile.php) and link to your Google profile, including the rel=”me” tag, in the Biographical Info box. (Make sure in your blog’s settings that your bio shows up on your author archive page.) For example, I include the following in my bio:
4. Go to your Google Plus profile. On the right side of the “About” page, where it says, “Other Profiles,” add a link to your author page on your blog. Google will add a rel=”me” tag to this link, so that your WordPress blog author page and your Google Plus profile are associated with each other.
5. Test it. Go to Google’s Rich Snippets testing tool and enter the URL of any blog post you’ve authored on your blog. If it works, you’ll see your Google name and image next to the search result.
6. This Rich Snippet structured data does not automatically show up in search results. You have to complete this Rich Snippets form to express interest in having Rich Snippets show up for your site, and even then there’s no guarantee Google will show them.