When creating a presentation you must take time into consideration.  The best way to judge time is to rehearse with a co-worker.  If your presentation is longer than an hour, you may need to insert a break.

Speak at a natural, moderate pace. Your tone of voice should be loud enough to be heard, but not at a yelling level.

Monitor you audience.  It is courteous for a speaker to ask their audience whether everyone can hear and understand what is being said.  During complicated sections make sure your audience is following the line of reasoning. 

If you are using a slide presentation with bulleted points, make sure you speak to each point on each slide, and expand where necessary.

If you are reading from a script, raise or lower your pitch for emphasis. If you are nervous, rehearsing will help because you'll know the material.