Don't expect to see all your students arrive in your course on the first day of the term. Problems with access, awareness, hardware, software, the Internet, connections, the phone/modem, the network, registration/enrollment, account creation, and so on will inevitably occur for your students.
At the beginning of the semester, encourage ALL of your students to get familiar with the specific learning management system environment for your course. Have a few warm-up activities designed to get everyone to know each other and to practice using the features specific to your online course environment. These activities will not only have them practice doing the kind of things they will be doing in your course, but can be designed to introduce the course and begin to support the development of a sense of class community.
Post an "ice breaker" discussion in the first module. Using the mechanisms for conducting an online discussion in your course, ask students why they took the course, what they know about the topic, what expectations they have, one thing they really hope to learn, etc. This will help everyone get to know each other, and you may gain insight into prior knowledge and expectations. You can practice and model a good online discussion, and students who enroll late, or have technical difficulties, will not be so far behind.
Consider creating a pre-welcome email message to have on hand, that you can forward to students as they appear in your course over the course of the first week.
Consider sending out an introductory communication to your students that specifies the first off-line reading assignments for the first couple of weeks. If students have technical problems they can do the initial reading, know what they should be preparing, and not be so far behind when they finally get online. You may also want to design the activities in your course for the first couple of weeks with this in mind.
Consider using a self-test type feature in your course development tool the first week of class as a comprehension check on the course information documents for your course. This “check” can ensure that students read the pertinent information and eliminate questions later on in the course. It also introduces the testing capability to students in an un-threatening way. Be responsive
Plan to login regularly and frequently —especially at the beginning of the semester. Students will be wondering "who is out there" and you can help them by responding right away. Set a schedule for yourself.
Respond to student email as soon as possible, especially at the start of the course. Consider using email for private communication between student and instructor. If student email is not private in nature, and better posted as question, or as a Bulletin Board item, ask the student to post it in the appropriate place in the course, so you can answer it once publicly for all to see.
Check for questions in your course regularly (especially during the first few weeks) and respond immediately to student queries. Consider directing students with technical problems the technical helpdesk, if you have one, so you don't become the tech support for your students.
Grade and return evaluated assignments to students as quickly as you can. Give students feedback on their performance and participation in your course early with suggestions on how to improve their work to meet your expectations.
If you experience technical difficulties . . . Contact your help source immediately, if you believe something is not working in your course, or if you notice some unexpected change.