A lot of acting teachers believe that public speaking and acting are very similar and I would beg to differ. What I find more credible are the similarities between public speaking and conversation. Yes, in both cases, you are addressing an audience; but, that is where the similarities end.
In acting, you are playing the role of another individual. And, your goal is not to interact with your audience but to entertain them. In public speaking, I would hope that you are entertaining as well, but your goal is to inform or persuade your audience and to be yourself, first and foremost.
What conversation and public speaking have in common is that you will (or should) get a response from your audience and indeed react to their response. Even if your conversation is just with another individual, that person is your audience. He or she is listening to you as you speak and may agree, smile, laugh, frown, or disagree.
That is exactly what happens in public speaking if you are engaging. And, part of the secret of dynamic public speaking is to engage your audience. You want to keep their attention. You want to get a reaction from them. Essentially, you want them to agree with you and believe in you.
Delivering a successful presentation means that you will speak to your audience just as if you were having a conversation in your living room. You are not reading an overhead presentation word-for-word nor are you delivering a rote, memorized script. You are talking to them, not at them. During a play, the actors are talking at you, not to you. They are giving a memorized delivery for entertainment purposes.
By addressing your listeners just as if you were in conversation, speaking with emotion, and making eye contact with your audience, you will discover 3 of the best means of effective presentation skills that do not resemble acting. Instead you will be holding a conversation. A bit more formal, but still a conversation.
In acting, your goal is to be someone other than yourself; whereas. in public speaking and in conversation, your audience expects you to be yourself.