Know your story, know your characters inside and out. Know what they had for breakfast, even though they’ll never eat on screen, and where they ate it. These bits of knowledge will help you totally understand your characters.
Have at least one, even 3 or 4 different projects in the back of your head. The last pitch I was at, I spent 5 minutes talking about the one I went in there to pitch, then 40 minutes talking about the numerous other projects that I was developing. Always have more ammunition ready so that it isn’t a wasted opportunity. These people want to know what you’re working on, but also what else you might be bringing to them in the future.
Be polite. Thank them for their time. Try and nail down an actual time when they say ‘we’re going to talk it over and we’ll let you know’… ask them, ‘Do you mind if I give you a shout next week? (or even pick a day that you’ll call them on)’ More often than not, they’ll say yes. They’re busy people, you’re project won’t be the only one on their mind, so talking to them in the following week reminds them that your project and you are worth giving some more thought to.
Hope that helps some.