I have collected these tips from attending numerous events and conferences, for example:
The Future of Web Apps in London.
Beyond the Printed Word in Dublin
SIME, Disruptive Media and Hubbub in Stockholm
LeWeb3 and LeWeb08 in Paris
Moving Images Malmö
Rework the World in Tällberg
Tällberg Forum in Sigtuna

The first two had a conventional setup with a moderator who introduced the speakers, and then let the speakers talk for 20-40 minutes, most of them using Powerpoint to illustrate their talks. I found that the majority of the speakers had interesting things to communicate, but the way they performed their presentation effectively eliminated most of the value for me in the audience.

SIME used a different method, relying on a moderator that held discussions with 1-4 invited speakers on stage. I find this approach much better, as it tends to focus on the issues and not on the speakers and the history of their companies etc. But it of course puts a lot of responsibility on the moderator who must be able to distill the value out of each speaker, but Ola Ahlvarson did a great job of this at SIME. The only thing I missed was visuals, displaying the websites etc as they are discussed. Using a combination of voice, pictures, video and text is always preferrable.

Since so many conferences suffer from these problems I felt that I must share my thoughts on how to hone your presentation skills. Comments are welcome, please help me add to this list!

The importance of presentation skills
It is very sad that so many influential, bright minded presenters with a deep expertise in their fields lose their audiences due to their poor presentation skills. It is also about respect for the audience. People pay a lot of money and travel from far away to attend conferences, so their time should not be wasted. Both the organizers and the presenters need to do everything they can to add value to the audience, so here are some useful tips.

For the professional speaker

Do’s

1. Think carefully before the event: what does this audience want to hear?
2. Hint: they are not interested in hearing how great you or your company are, they want to learn new things that can make THEM more successful.
3. Find a story about people (yourself and/or others) that illustrates your message and tell it with passion.
   Storytelling always beats lectures!
   
4. Start by urging the audience not to take notes, say that you will post your presentation online immediately afterwards. The presentation that you post should be complemented by short texts, speaker notes describing your pictures (since you show very little text during your presentation!)
5. Keep an eye contact with the audience, and move around the stage, don’t hold on to the speaker stand! Use a remote clicker to control your presentation. Remember that 70% of your communication is in your body language!
6. Speak slowly to increase the understanding and respect for what you are saying. Never try to cram a 30 minute speech into a 20 minute time slot!
7. Be visual, use pictures and videos that illustrate your points. Read my lips: less text, more visuals! You can do great presentations without any visuals,  but then you have to me a master storyteller.
8. Avoid monotony by using variation and surprises in your slide styles during your presentation.
9. Engage the audience! Ask questions and have them put their hands up. But don’t insult them with silly game play.
10. Focus on 1, 2 or maybe 3 things that you want to talk about. Explain the problem you are working with and then tell the story and visualise the solution.
11. Construct your presentation based on the classic drama: Start with a Set-up, then Present the problem(s), then proceed to the Confrontation and finally the Resolution. This has worked for thousands of years!
12. Hire a speaker coach that helps you trim you body language and voice.
13. Use a spell checker on all your slides. Takes only a minute, improves your image.
14. Use a dark background on your slides, as it is easier to read for the audience and better for the video cameras.
15. If you present in another language than your native, consult a language tutor to improve your pronuncation as much as possible. Getting your message out is about being understood and respected.
16. Test your presentation on other people beforehand and videotape yourself. Listen to their feedback and watch yourself: would you understand and appreciate your presentation?
17. End by showing a slide with a key question or action point aimed at the the audience, to encourage discussions afterwards. Also show you contact details and the link to your documentation on your blog or on an internet service like Slideshare. This documentation should NOT just be your slides from the presentation! Instead post special slides with your highlights explained with relevant post-analysis for the audience. Make sure that all the links to web sites that you have mentioned are active.

Don’ts

1. Don’t read word by word from your script. You will sound like a robot and miss the all-important eye contact with the audience. Instead use stiff cue cards with key words and starter sentences.
2. Don’t talk too fast and try to cram a 45-minute presentation into a 30-minute time slot by speaking at machine gun pace. You might just as well stay at home.
3. Never use acronyms without spelling them out and explaning what they mean.
4. Don’t read from text bullets in Powerpoint. If you have to use text bullets, keep them very short and very few per slide, then first let the audience read it and then, on your own words, expand on the subject.
5. Don’t use complete sentences in your slides. Your voice shall tell the story and the slides shall only support it.
6. Don’t start talking immediately on top of your slides. Let the audience interpret the slide for a while, then add your comments.
7. Don’t use hard-to-read fonts or garish backgrounds that obscures the text.
8. Don’t use cute or unusual photos that are not illustrating exactly what you are talking about. It distracts the audience, nobody will hear what you are saying.
9. Don’t use effects, such as texts that fly into the slide or ANY other disturbing transitions. You’re not running an amusement park, the interesting stuff should be in your content, not in your fireworks.
10. Don’t waste you audience’s time by presenting the history and organization of your organisation. Unless it is essential in order to understand your presentation, which is very, very seldom.
11. All essential facts mentioned need to also be visual. Don’t mention tips like “be sure to check out the website www.fancynewstuff.com, it has great features” without displaying a slide with both a picture of the web site and the URL in big letters + a note stating that the URL will be in your posted presentation.
12. Don’t hide behind the computer or speaker stand. Make sure the audience see you and maintain eye contact with them.

See also my post “Time for Conferences 2.0“.
I also recommend the presentation: Death by Powerpoint, it is useful!