As highlighted by J.V. Boettcher, PhD in Designing for Learning, the ten best practices for teaching online are:

1. Be Present at the Course Site
2. Create a supportive online course community
3. Share a set of very clear expectations for your students and for yourself as to (1) how you will communicate and (2) how much time students should be working on the course each week
4. Use a variety of large group, small group, and individual work experiences
5. Use both synchronous and asynchronous activities
6. Early in the term - about week 3, ask for informal feedback on "How is the course going?" and "Do you have any suggestions?"
7. Prepare Discussion Posts that Invite Questions, Discussions, Reflections and Responses
8. Focus on content resources and applications and links to current events and examples that are easily accessed from learner's computers
9. Combine core concept learning with customized and personalized learning
10. Plan a good closing and wrap activity for the course

For a complete discussion of each of these principles, see the complete article at Designing for Learning.