I was going to write a list of tips but I found this list at http://manwithnoblog.com/2007/10/30/tips-for-second-life-presentations/.  I think these are really useful tips if you are planning to present in Second Life.  Feel free to add any others you think of to the comments section - Deb. 

"When doing a presentation in Second Life:

• Don’t assume people will get the slides downloading on to the presentation screen as fast as you are.
• Don’t assume that they have their configuration such that the pictures render with the same amount of detail
• Don’t assume they have mouseview activated and have the presentation screen filling the entire HUD
• Don’t present with a standard Real Life MS-PowerPoint presentation layout. The screen can be small and fussy at best. Avoid text altogether if you can. (I like to see some text but prefer bullet points, the purpose of PowerPoint is only as a 'roadmap' or illustration of what is being spoken - Deb)
• Don’t assume everyone has audio in SL. Or that if they do they know how to configure it. If audio is essential for the presentation then make that clear in any SL or RL invite you issue. But be prepared to coach newbie SL avatars on how to configure audio.
• Allow for people without audio or slow internet connections. Be prepared to Issue a notecard with all the speaker transcript and references at the end of the session. (This is a very good point - Deb)
• Have someone as a shouter that shouts out the presentation, usually via cut and pasting from a notecard into the chat dialog. (I think there's an inworld tool called 'SpeakerBuddy' (or somemthing like that - I will check) that automates this process - Deb)
• Don’t have computers with separate microphones and speakers setup in the same room as you will get double, triple or even four times the echo of the talk. Even headsets can’t overcome this problem.
• Test the speakers audio setup before the presentation.
• Seating, don’t use the RL arrangement of seating like a normal layout, or set them far apart. Make sure they very close together in almost a tiered traditional speaking pit of amphitheater arrangement, or even like a large cube with the speaker at one end. You will be suprised the number of avatars you can get in small space. (Not sure that I necessarily agree with this - depends onthe type of gathering - Deb)
• Record the session in SL via tool such as Rogue Amoeba’s Audio hijack. (I haven't tried this tool but we would love to record the sessions, perhaps even to create podcasts in the future - Deb)
• Think about loading the seats with a script to send the avatars a notecard of the speakers transcript, pictures or any other object required.
• If you have promoted the event in the RL expect a good number of newbie SL avatars, allow for this.
• Be prepared to have a lot of avatars present (40-50) and remind people of techniques in decrease any lag time in Second Like. (tips for reducing lage can be found here and here - Deb)
• Position your avatar or camera so you can see the screen and the audience."