That's right, be yourself.
Isn't that what your mom said when you went on your first date? Well, momma's advice was right; it extends to public speaking and giving presentations too.
You want to show your personality.
Being natural should not be confused with lackadaisicalness, poor grammar, and wrong pronunciation or off colored speech.
Colloquial speech should also be avoid.
It is a goal to promote appropriate demeanor that enhances your credibility.
Oddly enough a person that is a natural speaker needs not to be too concerned with impressing their audience.
Speaking expressively helps to get the confidence of your audience.
If you are nervous or awkward in your delivery it will distract from the message you are trying to get across.
A natural, conversational style usually works best when talking to an audience.
Do not try to memorize your presentation or use a overly detailed outline you probably will become over dependent about the wording.
By doing this you may become stiff and your delivery will be too formal.
Develop ideas not in the exact wording; this will help your confidence level.
A warning of caution though, overly focusing on exact pronunciation will slow the nature progression of your presentation.
I have attended functions where people also sounded like an artificial robot.
The use of gestures should and can improve your presentations, but stiff and or overly emphatic gestures will detract and show nervousness.
Just be yourself and your naturalness will enhance your message.
Be sure to practice, practice and practice so more.