I'm into my third semester of online education. One benefit of some duration in this form of instruction is that I am gaining hindsight.
Based on my personal experience and what I am observing in other parts of the online universe, I have created "five major fails" for online education. Engage any one of these actions and odds are good that you'll crash your course and spike the dropout rate:
1) Be inconsistent. I have suffered through some of this personally, when I experimented with various lecture capture software during a course. On one occasion it might be SlideRocket, on another Snagit, and then finally Panopto once our university attained a license. Change ups during a course lessen the student experience. The framing of the information, and steps to access, may be different. Don't do it.
2) Be slow to respond. When you commit to being an online instructor, your moving into a 24/7 access world. Most of my students run on a different productivity clock that I do; I'm an early to bed, early to rise individual. They aren't. I make a points of checking last thing at night and first thing in the morning, and at all points in between. I stay connected with students to assure their progress in the course is not impeded based on my response time.
3) Underestimate the need for Internet and computer technology. Yes, I realize we're living in an always on, wired world. But please don't make assumptions when you roll out your online courses. Many of my students are adults and are returning to academics after a long hiatus. Some aren't computer savvy. One woman ran into the wrong sales rep at an electronics retailer and was convinced to buy a tablet computer instead of a laptop. She had consistent setbacks until she eventually dropped from our program. Specifically promote the need for a "modern" (you define it) desktop or laptop computer and high-speed Internet access.
4) Deviate from the syllabus. My stereotypical online student is an adult, has a full time job, has children and it trying to manage four courses a semester. A big success factor in the retention game is consistency and delivering the product you presented. I work in well defined weekly blocks which are provided at the start of the semester. The week's readings, assignments and forums are all contained in the block. My courses always rotated on the same time cycle, with assignments due every Tuesday prior to 9 am. If you want to contribute to chaos in your students' lives, consider changing course content and deliverables on a random basis; you'll form a disconnect and reduce trust almost immediately.
5) Remain aloof and arrogant. I am cautious about my professorial role as an online instructor. As one who returned to earn a MBA, then PhD quite late in life, I am aware of the fear that can accompany returning to the academics. It's no different today. One student confided she has a 30-year dream of earning a university degree; I must do everything in my power to help her climb that mountain. There is a fragile nature to creating a rigorous class experience, yet to coach and encourage in a gentle fashion. To that end, I strive to come up alongside students, rather than instruct down/at them.