Classroom training is a performance -- a vocal performance, like singing or acting. As a trainer, my voice is an important asset to my job, so protecting that voice is important.
One thing I've learned to do before class each day is to warm up, just like a singer warms up. Here's my routine.
Before warming up, I drink some water to make sure my throat is moist. Then I start by singing the musical scales (do-re-mi-fa-so-la-ti-do) up and down very softly. This acts as a diagnostic: I can usually tell pretty quickly how strong my voice is that day, if it's scratchy or clear, wavering or rock solid.
Then I add a bit more power, a bit more volume. I do some more scales, then go directly from low C on the scale (do) to an octave higher (DO) and back down again (do) a few times. I notice how quickly my voice was able to make the change, and how closely I "nailed" the note.
Next, I'll sing a familiar song, especially if the radio is on. This means singing notes in different order than just the scales. Again, I watch the transitions, looking for places where my voice may be a bit weak today. Then I know in the classroom I'll have to moderate my volume or I won't have a voice left by the end of the day.
Finally, I'll talk. I put a smile on my face and say, "Good Morning! Welcome to the Training Center. My name is Bob Watkins, and today, we'll be talking about..." I may ramble a bit about what we're going to cover that day: this helps me focus as well as lets me hear how I'm sounding.
I often do this warmup in the car while driving from the hotel to the training location. It looks funny, but when I hit the classroom, I'm ready to go. And, I don't run out of voice about 3 or 4 in the afternoon, as I used to before I adopted this warmup routine.