Public Speaking - Dress Rehearsal for Your Presentation

A few days before a play or musical opens, the entire cast and crew conduct a dress rehearsal. They do a complete run-through of the script on stage, dressed in their costumes, with the full scenery and lighting in place and the pit orchestra playing. The purpose of the dress rehearsal is to make sure everything goes smoothly on opening night.
The dress rehearsal is a great idea to borrow when you have to give a presentation. If you haven't presented in a while (or ever) or you've never presented to this particular audience (for example, the budget committee) or in that space (for example, the Boardroom), a dress rehearsal can make the difference between success and failure. Even if you don't get in costume or practice in the actual space, the point is to prepare for all aspects of the environment so nothing trips up your presentation.
Here are some things for you to think about in the dress rehearsal for your presentation:
ROOM LAYOUT
Where will you present? The room should be arranged so you can see everyone easily and so you won't trip over any computer cables or have to cross frequently in front of the projector lamp.
ROOM ENVIRONMENT
How are the lights and heating/cooling system controlled? If you're using a projector and screen, does the lighting allow the audience to see the screen and also have enough light to stay awake? What is going on in the room next door or outside the window? If you have to compete with a jackhammer, frequent sirens or cute kids on the playground outside the window, you should be prepared for it.
COMPUTER (if applicable)
How will you advance the slides? If you will be standing to deliver your presentation, I recommend using a remote control (inexpensive and easily available at office supply or electronics stores) so you are not tied to your computer.
Do you have a long-enough power cable or enough battery power? Have you disabled your computer's automatic updates so your computer is not automatically shut down and restarted during the presentation? (This actually happened to me a few minutes before I began a training session).
WHAT TO WEAR
Wear something comfortable AND powerful. To take an extreme example, pajamas are comfortable but they are not powerful. Clothes can help you communicate the professional image that you want to convey. And your shoes must be comfortable even if you're only presenting for a few minutes. Your clothing should have nothing you have to tug at, pull at, fix, etc., that will distract you or your audience.
PERSONAL PREP
Get enough sleep the night before you have to present. Make sure you have time to eat whatever food you need to present effectively - you don't want to be overfull, but you also want to avoid a growling stomach or light-headedness.
WHAT'S IN YOUR KIT BAG?
Do you have everything you might need with you - things like cough drops, antacids, other medicines, glasses if you get something in your contacts, etc? This is the time to think like a Boy Scout and be prepared. If you're speaking in front of the entire department, including management, at an offsite retreat, wouldn't you prefer to have your glasses with you in case you lost your left contact?
If you're not in your regular office building, who is your onsite go-to person in case you need something? When I was stung by a wasp for the first time in my life shortly before I had to present a workshop, I needed my on-site contact to get me medical attention quickly to ensure I wasn't having an allergic reaction (she was great and no, I didn't have a reaction).

Yes, thinking about these environmental factors and preparing for them takes time. But like a dress rehearsal, it's time well spent. As a result, you'll be comfortable enough with your environment so you can avoid preventable glitches and deliver your presentation effectively - and handle any unexpected obstacles with ease.