Have you heard the expression, "It's not what you say, it's how you say it"?
Many people who are reluctant to get up and speak fear the audience won't listen to them. They believe they're not witty, they can't tell a joke, and if they're not funny, nobody will pay attention. They believe they don't know enough about the subject and the audience will sense it and tune them out. Or worse, they fear the audience knows more about the topic than they do and will be sitting in judgment and finding them wanting.
All of these beliefs are false.
The secret to giving a speech worth listening to is not difficult or complicated. Simply ask yourself this question: "What is the great benefit the audience will receive from spending this time with me?"
When you speak to a group of any size, you have a job to do. You have a gift to give the audience. Your gift is the knowledge you have that they need. Your job is to focus on them and make sure they receive your gift so that they'll leave the room knowing more than when they walked in.
That's all there is to it.
How do you do this?
Research the organization or group that you're speaking to. What is their point of view, their reason for existence? Are they there because they want to be or because they have to be? Ask yourself, "What would I want to hear that'll make me happy if I had to sit here and listen?"
It'll help if you pepper your speech with ideas or subject matter they're somewhat familiar with as a lead in to new or controversial ideas. Find colorful explanations for difficult ideas, and don't be afraid to tell stories to illustrate your points. Let in as much humor as you feel comfortable with but let the humor come naturally from your stories. Unless you're a great joke teller, leave the jokes for Saturday night with the gang.
Audiences don't want to work too hard to understand you. Do you all speak the same language? Does your audience speak as well or better than you do? Do you have a strong accent or are you planning to use a vocabulary that's unfamiliar to them, i.e. technical jargon or slang? If their native language is different from yours, will you need a translator? A signer for the hearing impaired? The easier it is for them to understand what you're saying, the more successful you'll be. A major part of the success of your speech depends on whether or not your audience is able to receive it.
If you're the star of the show speaking to a sympathetic audience, it'll be easy to present your subject straightforwardly and enthusiastically, encouraging them to come along with you on this exciting ride. If you're presenting a controversial or oppositional topic, you'll make choices that take into account possible disagreement and be ready to counteract any hostility you may encounter.
Either way, the more you know about the audience and what they're hoping to learn from you, the more they'll pay attention and be happy they came. You're their magic key to getting the information they need to move forward. Your gift to them is to give them what they came for.