The best thing you can do in preparation for a presentation is be well rested. Your body and voice need to be rested. Do not go to a concert or sporting event the night before and scream your lungs out. Try to get a good night sleep.
If you are traveling or otherwise don’t have complete control over your sleeping and waking hours, find a little time to take some meditative rest before your presentation, even if it is only 5 to 10 minutes. Close your eyes and breathe in for a count of three, hold your breath for a count of three, and breath out counting one, two, three. Repeat. Do this while thinking about the message you need to deliver to your audience: not how you want to say it, just the short message that they need to GET. This wil focus and refresh your thoughts.
Once you have “RESPECTED” everything else on the Preparation list, stop obsessing, forget about it, and just get some rest.