Someone once said that "attitude determines altitude". That is quite true in every area of life but no place is it more true than when you are about to present your ideas in a public venue. The single most helpful reminder in preparing to present is to follow the motivational speaker Zig Ziglar's advice and take a "check-up from the neck up" before your presentation.
First, value your skills as a presenter. In a corporate presentation, you are the medium through which vital information is conveyed. If you don't feel good about yourself as a speaker, your verbal and non-verbal communication style will reflect your attitude and your audience will likely not feel good about you either.
Second, value the message you are about to deliver. Every time you present, you are presenting something of value for participants in sharing ideas and delivering information they need for success. Therefore, you must believe in the message in order to deliver it with enthusiasm. I have seen speakers who are so bored with the information they were presenting that the presentation had no effect whatever on the audience. If you are not convinced that the information is worthwhile for a corporate or public presentation, try conveying the information through a channel other than public speaking.
Want to be a good corporate or public speaker? Follow Ziglar's advice. Before hitting the stage, hit the mirror and take a "check-up from the neck up". Believe in yourself and your message. Then go, break a leg!