Just recently I've embraced the practice of doing things wrong on purpose. I will walk the student through a hands-on instruction and show them the wrong way based on common mistakes students or I have made in the past. Then I stop, and usually say, "Oops." I ask them why I failed. Discuss solutions and demonstrate problem solving in order to find the best way to achieve a goal. I've found this technique brings a bit of humor to the class. It definitely teaches them problem-solving skills. As an added benefit, when i do make new mistakes, my students don't really know if I'm doing it on purpose, but we'll discover the solution together.