This post is out-of-date. Google no longer makes this possible.
Set up a profile with Google+
It needs to be a personal Google+ profile. Business pages don’t have a Contributor section
Verify your email address
In your Google+ profile add your email address to your Contact Information, and then click the Verify button. Ideally the email address you use is on the same domain as your website.
List your website in the Contribute to list
In your Google+ profile go the Links section on the About tab and add your website to the Contributor to section.
Sign up for Authorship
Go here: https://plus.google.com/authorship and add your email address in the box (you need to be logged into Google to see the input box), and then click the button at the bottom.
Link your Google+ profile to your content
On your website add a link to your Google+ profile like this:
This can sit in the footer of your website, alongside any other links you have to social media profiles. The important bit is to include the
EXTRA: Add an author link to all your posts
On all the posts on your website you can add a byline for yourself. In WordPress you can include this line in the template file of your blog posts:
Posted by: <!--?php the_author_posts_link(); ?-->
This will add your name, a link to a page with all the posts you have written, and – crucially – it will also add the
rel=author tag to the link. More proof that you are the author of your posts.
If you also have a Google+ business page
Link to it too from your website, but make a distinction between the two links. Make the business one prominent, and stick the personal one somewhere in the footer.