Often in coaching presenters I watch them approach their content as if they were 8th graders assigned to give a report on their "topic". They visit Wikipedia and Google and clip art galleries to amass piles of information, factoids, job aids, video clips, and PowerPoint shows, then try to compress it into a 75-minute session.
Here's a model I like to use in developing my own presentations, and in helping others develop theirs. The trick: rather than starting from a lot of information and finding a way to deliver it in the available time (the result: lecture + bulleted slides), find your critical "20%". What are the 2 or 3 key takeaways? If I ran into your attendee 2 weeks from now, what would they say were your 2 key points?
In other words: Using this model, start in the middle and work your way out:
Remember: Design is done when there's nothing left to take out.