How to change the order of elements within a post?

Something like (in your single.php)

<?php while (have_posts()): the_post(); ?>
  <article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
    <time class="post-time" datetime="<?php the_time('Y-m-d'); ?>"><?php the_time('F j, Y'); ?></time>
    <?php if (has_post_thumbnail()): ?>
      <?php $thumbnail_image = get_posts(
        array(
          'p' => get_post_thumbnail_id($post->ID),
          'post_type' => 'attachment',
        )
      );
      ?>
        <p class="thumbnail-caption"> <?php echo $thumbnail_image[0]->post_excerpt; ?></p>
      <?php the_post_thumbnail('full'); ?>
    <?php endif; ?>
    <header>
      <h1 class="post-title"><?php the_title(); ?></h1>
    </header>
    <?php the_content(); ?>
    <footer>
      <p class="post-tags"><?php the_tags(); ?></p>
    </footer>
  </article>
<?php endwhile; ?>

I haven’t tested the image caption bit: let me know if it doesn’t work, or if you don’t dig the markup.