Classroom Management Tips

I would like to compile a list of best practices from fellow bloggers of your best classroom management tip for new teachers. Please leave one tip, your grade level and the State in which you live. I think this might be fun. I am new to blogging so I am trying to get started, thanks for your patience and support! I just completed my 3rd year of teaching and they always say, "Don't smile until Christmas!" - Do you agree with this tip for your classroom management?