1st post of Wordpress outside of loop.

first-post-seperate.php

<?php 

  query_posts('posts_per_page=6');

  if (have_posts()) {

    // do first post
    the_post(); ?>

    <!-- HTML for first post -->

    <?php while (have_posts()) {
      
      the_post(); ?>
      
      <!-- HTML for rest of the posts-->
      
    <?php } // endwhile
  } ?>