School Library Journal has a great article: Stir It Up that has a list of things you should NEVER do with teenagers at your library.
Because it is written so bluntly, you can immediately see why you shouldn’t do something. But check yourself, are you doing some of these things? When I worked in a larger library with other staff who had issues with teens and their behavior, this would have been a very handy way to start a conversation about why they were having problems with the teen patrons we had.