Many professional speakers use their hands when they speak to emphasis points. Using a headset allows you to act and speak more naturally. Tell the truth. Hosts value real experiences so use some stories from your own life to embellish your message. If you have experienced a personal struggle or triumph, tell the story and be sure that it is relavent to the topic you are there to talk about.
Hosts also value brevity.
Keep your comments as brief as possible and give them the opportunity to ask more questions. Take a breath now and then. Make every word count. You would be wise to rehearse answers to questions that are frequently asked. Be prepared but don't sound canned.