If you’ve decided to include a Google+ button on your WordPress site, it’s also suggested that you add a few new meta tags to your header so that you can customize exactly what appears when people share your page on Google+. You can read more about the requirements at http://www.google.com/webmasters/+1/button/.

Here is a quick snippet that you can add to your theme’s functions.php file that will add your post’s title, excerpt and featured image to the appropriate meta tags:

 * Add Google+ meta tags to header
 * @uses	get_the_ID()  Get post ID
 * @uses	setup_postdata()  setup postdata to get the excerpt
 * @uses	wp_get_attachment_image_src()  Get thumbnail src
 * @uses	get_post_thumbnail_id  Get thumbnail ID
 * @uses	the_title()  Display the post title
 * @author c.bavota
add_action( 'wp_head', 'add_google_plus_meta' );

function add_google_plus_meta() {
	if( is_single() ) {
		global $post;
		$post_id = get_the_ID();
		setup_postdata( $post );
		$thumbnail = wp_get_attachment_image_src( get_post_thumbnail_id( $post_id ), 'thumbnail' );
		$thumbnail = empty( $thumbnail ) ? '' : '<meta itemprop="image" content="' . esc_url( $thumbnail[0] ) . '">';
<!-- Google+ meta tags -->
<meta itemprop="name" content="<?php esc_attr( the_title() ); ?>">
<meta itemprop="description" content="<?php echo esc_attr( get_the_excerpt() ); ?>">
<?php echo $thumbnail . "\n"; ?>

<!-- eof Google+ meta tags -->

Now you can use the code supplied on http://www.google.com/webmasters/+1/button/ to included the Google+ button wherever you want on your site. I stuck it into the single.php file next to my other social media buttons. You can see them all below.