Know how to use email, including attachments. Understand the minimum hardware and software configuration and do not attempt to undertake the course without ready-access to this equipment. Research the course. All online training is not created equal.
Some courses deliver nothing more than the text on web pages.
Apply what you know about good instruction to online courses offered. Make sure you have convenient and reliable access to the Internet. Be sure you understand any other pre-requisite skills and knowledge that might be required in the course. Elicit the support of your colleagues, family and friends before you start out on your online adventure. Contact the instructor if you are unsure of your abilities to meet the demands of the course or have questions regarding the course.