No matter how good you become at laying out clear expectations, understanding will never be automatic. You have to check.
Check to make sure your team member understands the assignment before you part company. You both should have the same idea of what will happen, when it will happen, and how performance will be measured.
Follow up and check to make sure that the understanding turns into performance.
This is only one of 347 tips in my ebook, Become a Better Boss One Tip at a Time.