Is your teaching getting boring, even to you?
Here are a couple of tips that work for me:
Instead of teaching only the subjects in which you are "degreed" or certified, try adding two or three other subjects to your repertoire. Begin by adding a subject in which you did well at school but may not have studied for a few years. Practice online using free academic sites. If necessary, buy a teacher or parent copy of the textbook that includes the answer sheets. You may have to pay full price for this, but it is worth the investment. It is stimulating to you to have to be assessed for your achievements. It will automatically make the class more profitable for your student because you, as a teacher, have gained a new confidence in your own skills.
Secondly, try teaching a small group - perhaps just two or three individuals at the same time. The students can bounce ideas off of one another. Also, the "class" can play a few games when competition is at hand. If possible, add some "hands on" activities occasionally. This helps create a new enthusiasm for the subject.