Using .tpl Template Files in Custom Drupal 7 Modules
In Drupal 7 the theme and template layer can easily be over complicated, but this is the quickest and most effective way in my opinion to get started using template files in your custom modules. Get in the habit of using a template file instead of putting pieces of HTML inside your module code. This system is pretty flexible and you can create a template for a small item or for a whole page.