Successful preparation for online learning is not significantly different from classroom preparation. As with any new concept, however, it is important for an instructor to communicate how existing practices integrate with a new concept (in this case, learning online).
High dropout rates are not a function of the online learning environment - they are a function of poor course design, lack of instructor familiarity of the environment, and learner preparation. Preparing learners to learn online is perhaps the greatest skill that we can offer.
In an era of "lifelong learning", skills for acquiring knowledge play a greater role in success than do knowledge concepts (as they often cycle to obsolescence).