Clearly communicate to students your goals for any assignment or learning activity. Don't assume that students will know what the pedagogical purpose of the assignment is. Have a discussion about your goals and desired learning outcomes, and help students understand how specific aspects of the assignment fit these goals. Be open to making some changes if students have ideas to offer. After the discussion has taken place, summarize it and post it in the learning management system for students to revisit as they work on their assignments.