How to determine if theres a next page

You can use get_previous_posts_link and get_next_posts_link
to determine if they exists like this:

$prev_link = get_previous_posts_link(__('« Older Entries'));
$next_link = get_next_posts_link(__('Newer Entries »'));
// as suggested in comments
if ($prev_link || $next_link) {
  echo '<ul class="navigation">';
  if ($prev_link){
    echo '<li>'.$prev_link .'</li>';
  }
  if ($next_link){
    echo '<li>'.$next_link .'</li>';
  }
  echo '</ul>';
}

Hope This Helps