http://www.huffingtonpost.com/entry/3-meeting-survival-tips-for-introverts_5632b982e4b063179911ddda
Write your thoughts in advance. Get the agenda and think about the points that will be covered before the meeting. Write down your thoughts to help you remember them and to help you relax when the meeting begins.
Experiment with speaking before you have the perfect words. It will probably go better than you think. Part of what happens for introverts is that our love of thinking can lead to overthinking and perfectionism. To prevent that, we have to err on the side of talking before we feel ready. In reality, we usually do just fine. After all, you’re doing just fine every day when you speak naturally in conversations.
Ask for time to think. Accept that sometimes you simply need time to think and that it’s okay to say so. You might say, “I’m hearing some good points. I have some thoughts brewing about it and would like to come back to that a bit later.” It might feel awkward at first, but both you and they will be fine. Really. I carry this idea that helps me in those awkward moments: “Be you and the world will adapt.”