Getting the outcomes right before you start writing will make things easier for you. If you’re writing the last chapter, and find out that some of your outcomes aren’t appropriate, you have a lot of rework to do.
Make some exercises that students should be able to do at the end of the course. Create them even before you finalize your table of contents. Do the exercises yourself. Even better, ask less skilled people to do them. Can they? What do they have trouble with? Doing this early can save you a lot of pain later.