A simple Ajax pagination with only one button forward. Click to get more posts without reload the page, click again to get more, again and again, unti
Just make sure your layout agree with the good pratices for theme development and uses the traditional navigation links previous_posts_link() and next_posts_link(). If yes, your theme is ready to work.
Try to read the theme HTML code to confirm the selectors used here, if different, set here the css selectors you found on it.
Sometimes the Theme put some extra elements inside the content area. To remove this, search the theme HTML code for the elements you want to remove, get the css selectors of its and then put all that extra in the option "Extra content to remove". If you got problem, try to read the Selectors documentation from jQuery.