Previous and older set of posts links

The other question is completely wrong and should not be used

• previous_post() and next_post() is both depreciated functions and should not be used anymore

• Never replace WP_Query with query_posts to solve a problem. This actually creates more. Also, query_posts should never be used

• showposts is also depreciated in favor of posts_per_page

To make pagination work, you will need to do the following instead

• Set the paged parameter in your query arguments (paged=$paged)

  $paged = (get_query_var('paged')) ?get_query_var('paged') : 1;
  

• Use previous_posts_link() and next_posts_link() to paginate your posts

• Set the $max_num_pages parameter for next_posts_link() as to correctly calculate the amount of pages when using a custom query

Your query should look something like this. (Taken from the codex)

<?php
// set the "paged" parameter (use 'page' if the query is on a static front page)
$paged = ( get_query_var( 'paged' ) ) ? get_query_var( 'paged' ) : 1;

// the query
$the_query = new WP_Query( 'posts_per_page=5&paged=' . $paged ); 
?>

<?php if ( $the_query->have_posts() ) : ?>

<?php
// the loop
while ( $the_query->have_posts() ) : $the_query->the_post(); 
?>
<?php the_title(); ?>
<?php endwhile; ?>

<?php

// next_posts_link() usage with max_num_pages
next_posts_link( 'Older Entries', $the_query->max_num_pages );
previous_posts_link( 'Newer Entries' );
?>

<?php 
// clean up after the query and pagination
wp_reset_postdata(); 
?>

<?php else:  ?>
<p><?php _e( 'Sorry, no posts matched your criteria.' ); ?></p>
<?php endif; ?>