With this function/recipe you will change your core single.php file. If you have no information about WordPress coding -so you’re a newbie- you can get some support if you send a mail to me. Don’t touch your single.php if you don’t know about WordPress

We will change our themes single.php. Make bakcup and be careful. After backup open single.php and copy this code after loop or content.

Here is the code;

<?php
      //for use in the loop, list 5 post titles related to first tag on current post
      $tags = wp_get_post_tags($post->ID);
if ($tags) {
echo 'Related Posts';
$first_tag = $tags[0]->term_id;
$args=array(
'tag__in' => array($first_tag),
'post__not_in' => array($post->ID),
'showposts'=>5,
'caller_get_posts'=>1
);
$my_query = new WP_Query($args);
if( $my_query->have_posts() ) {
while ($my_query->have_posts()) : $my_query->the_post(); ?>
     <p><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></p>
    <?php
  endwhile;
  }
 }
?> 

Save single.php. And then refresh your page. Related Posts are display after content. :) If you change ‘showpost=5‘ (the 5 is post number) 5 to 4,6,9,etc. Related posts number will change.

That’s All! Have a nice day!