WordPress secondary loop

wp_secondary_loop.php

// video source http://wordpress.tv/2013/03/15/andrew-nacin-wp_query-wordpress-in-depth/
// presentation http://www.slideshare.net/andrewnacin/you-dont-know-query-wordcamp-netherlands-2012

$q = new WP_Query();
while ( $q->have_posts() ):
    $q->the_post();
endwhile;
wp_reset_postdata();

// or in the template functions.php
function mz_my_template( $q ) {
    // always check to avoid modifying main query
    if ( !$q->is_main_query() )
        return;
    if ( !is_page_template('my-template.php') )
        return;
    $q->set( 'author', -5 );
    $q->set( 'posts_per_page', 25 );
}
add_action( 'pre_get_posts', 'mz_my_template' );