You only get one chance to make a first impression.
Remember, the audience is not thinking about you; they are thinking about themselves. Therefore, THE PRESENTATION IS NOT ABOUT YOU, IT IS ABOUT THE AUDIENCE. Get over yourself. Just before the meeting, look at yourself in a mirror and remind yourself there is nothing you can change other than to straighten your clothing and comb your hair, so stop worrying about yourself and focus on the audience.
Physical appearance is important, but don’t drive yourself crazy worrying about things you can’t do anything about.
If you can learn to feel good about yourself, you won’t be worrying about how you look. Have your clothes pressed and get those ties and scarves straight. Dress for success and dress for the occasion. This means that, whenever possible, you will be more “dressed up” than the audience. For example, if the dress code is “dress casual”, you should be dressed just a little bit better than “casual”. It is important to look and feel like the person in charge.
Give your problems away to the audience! If you have spilled coffee on your shirt or lost a button at the last minute, get it off of your mind or you won’t be able to concentrate on anything else. I suggest using humor. I would tell the audience that I spilled coffee and make a joke about it. By acknowledging the problem (or giving it away) I eliminate it from my mind. I no longer worry whether or not the audience notices the problem because I have told them about it. Remember, human nature dictates that the audience is going to be thinking about themselves, not about you. You are the only person in the room worrying about you. Get over yourself for a few minutes and you will be able to focus all your energy and attention on the audience and the information you are presenting.