Memorize every word, word for word, in the Airplane Flying Handbook. Then you can just start reciting from whatever chapter applies to the maneuver you are introducing. That, or you could just say what you are doing and what you are noticing. The guy above has a good idea. When I was working on my CFI, I would practice teaching maneuvers while driving my car. It takes something you are familiar with, driving, and combines it with something you are trying to get good at, talking and making sense. I would start with what the maneuver is and a short reason why we do it. Then I take it step by step, noting what I am looking at while doing the maneuver. Hope it helps. You'll notice after you get a bit of instructing experience that explaining maneuvers isn't hard because you are much more in tune with flying the airplane and what you are looking for.