Michael has a great short list of tips for giving presentations at library conferences. I agree wholeheartedly with everything he says [especially being prepared to do the material cold, and sitting through other speakers]. I even have a few more points based on my experiences...

1. Being well-prepared includes being mindful of time limits. Even if you have a normal stump presentation, try to tailor it for the time you have available. It's good practice for you and polite to your audience who often has many presentations to attend.
2. I always tell people to raise their hands if I use words they don't understand. This reminder gives me a chance to informally talk to an audience beforehand and lets me know if I'm misjudging their level of knowledge.
3. Offer multiple ways for people to talk to you after your presentation. Not everyone feels comfortable asking questions in front of a large group, but if you stick around afterwards, or make your email/IM/web address clear, they can follow-up with you. I also put all my talks online so people can refer to them, or click through some of the links I had later on.
4. I always try to thank the people who invited me or otherwise facilitated my being there. Conferences are often stressful for everyone involved and trying to be affable and low-maintenance as a speaker, as well as appreciative as an attendee afterwards can help ensure that you are invited back.