Participants take online courses via computers and mobile devices. Given the various apps, projects, and meeting reminders that are contained on these devices, the potential for distraction is high for trainees.
To keep everyone on task, use short, interactive quizzes, preferably with a variety of answer types such as multiple choice and labeling. That will help ensure that trainees remain focused by allowing them to directly engage with the content. And as it turns out, just knowing that there are quizzes will aid with the retention of the material, thanks to a phenomenon known as the Hawthorne effect.
On a related note, consider the tone you use in training materials. When you're not catering to a live audience, training materials can have a tendency to come across as dry and impersonal. If you have a photo of people in view while creating courses, it makes you think of presenting live, which will make the tone more conversational and, thus, give trainees a sense of interactivity. Remember that you don’t have to make e-learning a complete replacement to live training; a bit of live training is a nice complement to the online counterpart.