With conventions of this magnitude, it would be extremely difficult and disorganized to have 2 or 3 volunteers jumping around through the hall in order to give the microphone to the audience members with questions.
Because of this there are specific points with microphones. If you have a question, simply go to the microphone. It is to your advantage to have the question in English. Maybe the star happens to speak Spanish, French or something else, but the other audience members would also like to understand the question. If you don't speak English, simply ask your neighbour or someone else in line if they can ask your question for you.
General Information about Panel Questions:
Don't ask for a hug, autograph, kiss, or other similar things. The questions should also be formulated so that the actor/actress can give an open answer (that is, no simple yes/no questions).
Please have a certain amount of respect for the star. Questions like "are your boobs real?" really shouldn't happen, but they do come up fairly often.
Please don't pander to any minority groups. At Bloody Diaries, everyone is treated the same. So you don't need to tell the star that they should sign your tattoo, your baseball, or a picture for your girl friend right now. It is also not interesting at this point, if it's your birthday, you're a homosexual, or if The Vampire Diaries or THIS specific star has influence your life.
Such things will make you very unpopular and could be embarrassing or awkward for the star, who will probably not want to refuse your request.