1. Rehearse.
2. Anticipate pitfalls.
3. Break difficult material into the simplest possible components.

If you can't do it, there's no way your students can do it. But even if you can do it, they probably still can't do it without a lot of help. Put yourself in the shoes of a crackly-voiced 18-year-old who's played guitar for two years, figure out what spots will be tricky for him, and design sub-exercises to reach your goal. There is no harm in doing a simple exercise well, but there is no point to doing a complex exercise poorly (thus spake the grumpy pedagogue).

---Ness