When you first start to design, you have to think of one MAJOR element. Your audience. Knowing your audience is a key element in having a successful website. A good example of how to design for your audience comes from National Geographic.
Their regular site is definitely geared for an audience that is more mature audience that definitely has a passion for learning. The navigation is thorough and easy to find. Each section of their navigation leads to a different audience. When you click on MUSIC, it takes you to a page that is targeting a younger audience than the main page. It has very urban, hip hop elements that keep this section young and fresh.
Their KIDS section is perfectly appealing to that very young age. Bright colors and games are just what kids want. The navigation is completely different. It is on top and has images to help communicate with that young audience. Even the advertising at the top of the page is entertaining. There are little frogs jumping across the screen. This page has what it takes to keep a kid occupied and entertained.
The HISTORY page isn't that much different than the main page. But what it does, is very subtle. It has several textures that are applied to create this sense of time, and its effect it has on the site. It definitely grabs hold of the history buff type.
So, I am not going to go through every page and discuss it with you. But I can ask you to go through their site and decide yourself on who the audience is for each page. You might even learn something interesting while you are there.