Think about your potential audience and what you want them to do when they come to your website. Then think about what the site needs to do to help them achieve it.
Create a visual Site Map of your website and decide how the content will be grouped. Also determine what functionality the pages will have and what kind of navigation system you'll be using. Consider usability as well as design, and get your client to approve a Site Map before starting the design work.
Designing and building a successful website always starts with solid, thoughtful planning. Consider all the elements that'll appear on a page before beginning site construction.