I know it should go without saying, but I thought everyone would prepare for a job interview too. Before the meeting, understand what is the purpose, who is going to be there, and what they expect out of you. Someone is organizing or calling the meeting. If you have any uncertainty why you're invited, ask that person what they expect you to contribute to the meeting. (By the way, if they say you are there to observe, that's a bad sign. It means there are likely to be a lot of other people in the meeting with no purpose. If you are there 'to learn', that's a little better, but I would bet you could learn whatever it is in about a tenth the time outside of a meeting).
And if you are expected to deliver or review or present something, make sure you do it ahead of time. If it's really important make sure you go over the material you are responsible for with your boss or a peer, until you feel confident that you understand what they're expecting and are comfortable with the other people who are present.
