Structural Integrity:
An online course environment should not pose a barrier to learning. This can only be achieved by providing a logical organization, clear unambiguous instructions and investing in careful ongoing course maintenance. Here is a helpful checklist:  
Organization
Page titles accurately describe the contents
Labels, titles and subtitles for repeated information are consistently applied.

Course content is organized so that students can reach their destination in as direct a manner as possible (see samples).  
File sizes are kept to acceptable standards for sending, downloading, and viewing
Files are compatible with the software used by the widest range of users.
Instructions
Instructions are clear, concise and up to date
Expectations have been set for the course
Advice is provided for completing specific activities
Directions are provided for completing online activities
Assessment criteria are provided for assignments, exams, quizzes, etc.

Also See:

Sample Discussion Thread

Sample Assignment

Sample Lesson Page