The fact is, variation will arrive organically when you are truly connected to your material and you are — as we say in the acting world — in the moment.
Just think of how a kid tells a story when they’re excited or in a state of wonder.
I had an Alexander Technique teacher years ago who used to say “let,
allow, permit” when it came to how we moved on stage.
The same is true for speaking. Rather than force a
tone, let it happen organically. On top of this, it’s critical that you are connected to what you are saying so that you never are out of sync with your content. Quiet moments should elicit a quiet tone. Excited moments should bring an excited tone.
But all this will come if you structure your presentation so that you have a full spectrum of
experiences within it and then you reconnect with those experiences. If you do, you will have more
variety than you can possibly imagine because inside of you is a full prism of colored light just waiting to shine.