Pagiantion problem (Not showing next and previous link)

i am newbie in wordpress. i am referring link for pagination and trying to put next and previous link to posts list. but i am not getting next and previous link in my page.

What’s going wrong in my code?

[please mark any posted code – http://codex.wordpress.org/Forum_Welcome#Posting_Code ]

<?php get_header(); ?>

<h2>Hi this is index file</h2>
<h1> Post List</h1>
<?php if(have_posts()): while (have_posts()) : the_post() ?>
<h2> <?php the_title(); ?> </h2>
<h3> <?php the_author(); ?> </h3>
<?php the_content(); ?>
<?php endwhile; ?>
<div class="nav-previous alignleft"><?php posts_nav_link(); ?></div>

<?php else :?>
<?php _e("Sorry ! No post available"); ?>
<?php endif;?>
<?php posts_nav_link(); /////// ?>
<?php get_sidebar(); ?>
<?php get_footer(); ?>

i think i kept posts_nav_link() in wrong place.

Thanks in advance