Set the theme. Define very clearly what your presentation is going to be about. If you are marketing a product or an idea the best way is to choose a striking, single headline to the presentation.
Provide the outline. A presentation without a provided outline is extremely difficult to follow.
Guide your audience through the presentation. If you are opening or closing a section, mention during the transition.
Make sure that the whole presentation is very well structured. This is what a presentation is all about. You have to transfer your idea / results / product / strategy in the most intelligible and comprehensive manner. The key is to break everything down to manageable chunks and produce the cause-effect relationship.
