Common approach to design web page components layout

Starting to design web page layout from the scratch for a first time and want to know what's the best practice to set web page and all components on it measurements. The page will have horizontal header with a navigation bar in it and a three columns beneath it. That's what I've come up with so far:

• fixed hight for header part with horizontally aligned nav links
• fixed hight and width for web components
• components resides in a three columns (div elements) that has min-width set

Do I miss something or it's a good way to go?