Long presentations have all the same rules as short presentations, they just take that much longer to prepare for and present.
Begin with the end in mind. Give your audience a reason to listen. Paint a picture of how your presentation will improve their lives: improving business skills, helping them make or save money, showing them a more effective way of performing a task, etc.
Strike a visual-verbal balance. Many PowerPoint presentations contain charts and graphs to deliver data. While charts are important, you'll rarely hear your audience complain that your presentation had too few of them. If you show a slide that's heavy on data, follow it up with a visual slide that contains little, if any text. If one slide asks the audience to focus on a chart, try following it up with a slide that shows nothing more than an image. This will force the audience to shift its focus to you, the speaker. It will also give everyone's eyes a break.
Organize with 10-minute intervals in mind. Research has shown that our minds tend to wander after approximately 10 minutes. That means during your next presentation, members of your audience are going to tune out at regular intervals to daydream about what they're going to have for dinner or watch on television when they get home. So plan activities designed to draw them back that occur every 10 minutes or so. For example, introduce a second speaker who takes over a small portion of the presentation; insert video clips; ask a question of your audience and get a discussion started; engage them in an activity where they are required to think and write.
Read the entirety of this article at The Two Hour Plus Presentation.
Here is an example of a one hour presentation on how to improve PowerPoint presentations.
One way to add meaning to your presentation is to use images.