Generally you want to keep it back until your pieces are developed. If you bring it out early, your opponent can attack it while developing his own pieces at the same time. You have to spend your time moving your queen to keep her safe. Then your opponent has all his pieces out, and you're lucky if you haven't had to completely retreat your queen. That gives him a much stronger position going into the middle of the game.
There are times when it is appropriate, but when you are starting out you should try and keep her back while you get your knights and bishops out.



what I have always had a delema whether it is good to get your queen out into play early or let it wait intil all of your piecies are in play. franly I have no idea wich is better when i could see both having there own perks.