Perhaps the most daunting task is to plan a new course that will be taught entirely online, particularly if you have never taught online before.  Composing the syllabus, assembling the exercises and quizzes, weighing the criteria for grades - all this presents as set of unfamiliar challenges. The approach to solving such problems is similar to what you would use in a traditional classroom: setting the goals for the course, describing specific objectives, defining the required tasks, and creating relevant assignments.  Online courses differ in the technique.  

In a classroom, you have your physical presence, your voice, body language, intonation, expressions, gestures and eye-contact to help you communicate with your students. In online education, it is the written word that conveys the crux of what you want to say. This fact puts an inordinate emphasis on style, attitude, and intonation as they are expressed in print.

Online courses depend heavily on the participation of students. As an instructor, you will need to step back from the spotlight in order to allow students to take more active role. This will require that you fashion tasks and exercises that emphasize student collaboration and deemphasize the traditional role of the instructor as the central figure of the pedagogical play.   

The main idea here is that there is no need to start from scratch to teach online. You can apply what you already know and add to it by using new tools and techniques adapted for the online environment.