Site design takes a number of steps.  The challenge going through the steps is to not be thinking about the site itself, but to focus on the people who will be using it and the content they want. 

If you've been through the process of building a web site, creating a Drupal site is a bit different.  Many design processes start with layout.  With Drupal, or any content management system, it's best to focus on what you offer and to whom, not how it looks.  Not in the beginning, anyway.

Site design starts with defining what type of site you are building, then establishing personas.  Next, gather content then assign roles to manage that content. 

You'll find the steps in further detail under the Site Design portion of this site.