Tabs should be drawn correctly. For tabs to work to full effect, the graphics have to create the visual illusion that the active tab is in front of the other tabs. To create this illusion, the active tab needs to be a different color or contrasting shade, and it has to physically connect with the space below it.
Don’t make me think
Being an expert in online usability Krug gathered his experience in a wonderful book. This summary of key thoughts will help you to remember most important principles and laws.