Classroom management, to me, is the most important aspect of education. Over the past few years I've been in many different classrooms with teachers who all had different styles of classroom management. There were some great examples of classroom management as well as some examples of what to stay away from.
There is a common expression used by teachers which is "don't smile until after Christmas" meaning that you should never show weakness to the students until January. Classroom management doesn't need to be this way. I believe in laying down a set of class rules the first day of school and sticking to them throughout the entire year. There also needs to be consequences for breaking rules because students will always do certain things to see how much they will get away with. Everything must also be fair and consistent. The same penalty must be given to each student who breaks a rule. It is very important to never shown any type of favoritism in the classroom.
My philosophy is that 40 minutes a day will never be enough time to teach the students everything about chemistry so not a minute can be wasted. On the first day the students will receive a "Classroom Procedure" which will tell them what they need to do each day when they enter class. If they get in the habit of following these rules, they will continue this pattern for the rest of the year.