If you can't find a completely quiet place, go where at least it is comforting sounds, and sit down. Consider bringing a notebook or journal.
Start meditating, you can also sit in a yoga position if you would like or sit comfortably with your back straight
After clearing your mind, either free-think or else, if you have a topic in mind, focus on that. However, avoid dead end, angering, and solution-less subjects. Focus on subjects where you are certain you can find new ground and progress.