It all depends on your level of expertise, the students that you're working with, and the material you're instructing. If you're great with students and know the material like the back of your hand, you shouldn't have any trouble. But if you're shaky about a particular topic, you may want to brush up on your skills before teaching it or you could run into some issues. Furthermore, not all students have the same background knowledge or learning ability. This means you'll need to be able to adapt to each student's unique learning style to help them succeed.