<?php
if ($teaser) { 
  // node is being displayed as a teaser
  // Anything here will show up when the teaser of the post is viewed in your taxonomies or front page
} else { 
  //all other cases
  //Anything here will show up when viewing your post at any other time, e.g. previews
}
?>

  <?php if ($teaser): ?>
    <!-- teaser template HTML here -->
  <?php else: ?>
    <!-- regular node view template HTML here -->  
  <?php endif; ?>

<?php
if ($teaser) { //if node is being displayed as a teaser
  //Anything here will show up when the teaser of the post is viewed in your taxonomies or front page
} elseif ($page) { //if node is being displayed as a full node
  //Anything here will show up when viewing only your post
} else { //all other cases
  //Anything here will show up when viewing your post at any other time
}
?>