Add rel=next and rel=prev for all the paginated pages

Use the following code in your theme functions.php

    function rel_next_prev(){
        global $paged;
        if ( get_previous_posts_link() ) { ?>
<link rel="prev" href="<?php echo get_pagenum_link( $paged - 1 ); ?>" /><?php
        }
        if ( get_next_posts_link() ) { ?>

<link rel="next" href="<?php echo get_pagenum_link( $paged +1 ); ?>" /><?php
        }
    }
    add_action("wp_head", "rel_next_prev");