Bob Metcalfe (co-inventor of Ethernet and founder of 3Com) offers his tips to UT students on how to speak well when giving a talk:
Our daughter Julia just got promoted at Facebook and asked me for advice on giving talks. I hope she doesn’t mind that I’m sharing my advice with you. Listening is my real specialty, with writing in second place, but here is stuff that works in speaking; note that I have written it down: Speak on what you know. Prepare by collecting and organizing your thoughts in writing, say on 3X5 cards for small groups, 5X7 index cards for larger audiences (that’s humor), or Powerpoint. Start preparation by asking who your audience is and why they will be listening to you. Show respect by over-dressing your audience. Smile and say thank you. Summarize what you are going to say, say it, then summarize what you said. Speak slowly and clearly, pausing now and then at carefully chosen places, to let people process what you’ve said. If at all possible, take questions from the start and continuously through your talk. After promising at the start to end on time, end on time. End on time. Early is better.
Keep in mind that generally your audience wants you to succeed — they are rooting for you. Bless their hearts, but audiences generally do not realize that you can see them, so for impact make some eye contact and smile. Be funny, especially if the topic isn’t. Look at your audience when speaking to them — pick out friendly faces in the audience here and there, move your eyes from one to the other. If people start to tune out, notice, stop talking and ask if they are still interested or have questions, you do not want to waste their time.
When you make lists, three items is best. Start a list with your second strongest item, end with your strongest. When someone seems to want to ask a question, stop talking immediately, invite them, and reward them by listening carefully to their question, asking for clarification if needed. If someone asks a question you cannot answer, say the words “I don’t know” and make a big show of writing it down and promising to get back on that. If an audience member misbehaves, walk toward them and that usually quiets them down. Be sure to have fun speaking; audiences can smell fear. Get good at it by practicing — get gigs regularly. If someone makes a video of your talk, watch it twice and take notes on how to improve. Speaking is the most fun you can have standing up.