It's actually not as grim as I might put it, since usually, the audience is pulling for you. They want you to be interesting, captivating and persuasive. They like the feeling that you are in control and taking them along with you.
Remember this though: If you are speaking from a prepared text, a written speech - rehearse it, memorize it and condense it into notes so that you can deliver your speech to the audience, not down into the pile of papers which you are hanging onto for dear life.
I listened to a speaker at the Democratic National Convention who slowly, clearly and methodically read her prepared remarks. I listened hard and decided her words were worthwhile, but there was no passion behind them, she wasn't speaking directly to me, and as a result my mind wandered. I can't even remember who she was.
Think of all the elements that make up your delivery:
- Vocal pitch
- Facial expression
- Body language
- Speed (or lack thereof)
I'm sure this list misses things - it's simply to show you there are a number of things you'll need to work on every time you open your mouth. Can you remember your point, your words and make music out of them without practice and rehearsal?
Rehearse. In the car, the bathroom, while walking the dog and whenever else you make time. The importance of what you are saying and why you are speaking determines the amount of time needed practicing it. Would you do less when participating in a piano recital or sporting event?
The more you do it the better you'll get.