Great question! As educators, we need to focus on having clear expectations as well as maintaining the attention of our students so that we are not accidentally the reason they struggle with completing assignments.
Let me ask you this: when you write questions or create assessments, what is the purpose of what you are writing? Are you trying to teach while assessing or are you trying to create a very specific type of question to avoid confusion on your expectations?
In the first case, when writing your assessment tasks you should be focusing on what they have learned so far and what they need to demonstrate. An assessment task's purpose is primarily to assess and secondarily to teach. Perhaps, in this case, you are trying to teach them how to correctly complete the task or trying to explain the process you want them to demonstrate. To this, I recommend introducing the method/process during your lessons and allow them to become comfortable enough with the process that when they see an assessment task they instinctively know exactly what you expect of them. This will allow you to avoid the awkwardness of reminding them about your expectations during the assessment of their skills.
In the second case, it may be beneficial to break up your assessment tasks to focus on one thing at a time in a cumulative fashion. By building layers of complexity, going from general to specific, you will be able to shorten down on written chunks of instruction and will make the completion of your expectations less confusing for the student.
I hope this helped!