Instructional designers have a word for course organization. Chunking. I have a weird aversion to that word, and I'm a marketing girl, so I call it "packaging".
PACKAGE your online course - your modules and assignments. Make them nice and pretty, so students can neatly unwrap them.
Here is how you package an assignment:
Use consistent nomenclature, meaning give each assignment a dedicated number or name. Use consistency so students can easily find it.
Include VERY detailed instructions.
Include student-friendly learning goals.
Explain how the assignment will be assessed.
Explain how much time will be allotted to complete the assignment. Include the due date and time.
If applicable, give collaboration guidelines.
Explain the submission process.
Explain how they should proceed after they've submitted the assignment.
REMEMBER TO INCLUDE ALL ATTACHMENTS AND LINKS!