Begin your speech with a quotation, statistic, anecdote or question. These introductions can get the attention of your audience and help you keep it throughout the rest of your speech.
Write conversationally. Avoid using language that is too formal. Your audience will be better able to relate to you if you sound like you are a regular person instead of a scholar. You can still sound professional without sounding overly stiff and unapproachable.
Interject humor occasionally into your speech. Unless you are dealing with a very serious topic, humor can help liven the mood of the audience. Use it sparingly, though. If overused, humor can detract from your speech's thesis and arguments.
Use your introduction to tell the audience briefly what you are going to discuss. Then use the conclusion to tell them what you said.
Connect the audience to your topic in your introduction. Tell your listeners why they should care about what you have to say. In your conclusion, bridge your thesis and arguments to the wider world and give the audience ideas on how to take action on what you have discussed.
Write your speech to let your personality and enthusiasm shine through. Your passion for your topic should be evident throughout the speech. Audiences are more likely to be engaged in a speech in which the speaker is genuinely interested in what she is talking about. When you display confidence in yourself as a speaker by writing in a tone that is genuinely "you," your audience will latch on to it and be interested in what you have to say.