Legibility is key. Make sure your content can be read and understood. View your site using different browsers. Visitors should always know the context in which they are currently operating. Help users to know where they are, where they have been, and what they have accomplished.
Consistency means predictability.
Avoid errors in both content and mechanics. Just as any individual instructor's course will have a unique look and feel, so should an instructional Web site have a special look and feel. The appearance of the Web page must match the purpose of the page. Various kinds of pages should have different kinds of layouts. A syllabus will not have the same layout as a study guide.