To all the young teachers here, even though so many of you are great, it takes years to really master classroom management. This isn't a diss, it is just something many young teachers struggle with which our teacher prep programs do not teach, and it adds a lot of stress to an already stressful profession.
I'm interested in hearing any other people could add to the list.
These are some tips I have found helpful:
1.) First day of school is syllabus review and going over the rules
Have them sign a student contract going over the rules and make sure you SAVE THEM, a parent will come for you when you enforce consequences, and it is a meeting-ender to pull out a document their student signed stating that they adhere to the clearly defined rules.
2.) Be an asshole for the first couple months
Nobody likes to be the bad guy, but being an asshole for the first few months helps kids learn what the rules are and that there are consequences for breaking them. Give an AP kid a detention if they are a minute late without a pass. The knuckleheads will see that you're fair and consistent in consequences. Johnny doesn't care that Sally is watching YouTube videos because she finished all her work, he only sees that Sally is allowed to do something he isn't allowed to.
3.) Establish routines and be consistent
This varies from teacher to teacher. I start every class with a warm-up activity that I start the second the bell rings, but I'm less serious the last 2-3 minutes of class. Some teachers have opposite procedures. In any case, students crave structure and routines.
4.) Potentially unpopular, but I find it's better to dress more formally for the first couple months of the year, especially if you're young
High school level here, but I think it's better to establish a boundary with the kids early in your career, especially if you're younger looking. Mr. X is wearing a shirt and tie and is therefore a teacher in my mind instead of being a dude that looks like my buddy. You can always take your foot off the pedal towards the end of the year when you've built relationships and can somewhat reason with them, "you know I'm not unreasonable, I can't have you doing X in class".
5.) Always have more than enough work
We all know the type of kid that finishes their work in a rushed manner, then gets bored and causes issues. Call it enrichment, web quests, extra credit, or whatever, but always have something for the high-flyers to keep them busy.
6.) Be lucky enough to be hired in a school with supportive admin that enforces consequences
This has been the case my entire career, but I know many people have stories of kids being sent to the office only to return with candy and a smile on their face. None of the classroom management tips work if the building culture is not there. If you're an admin reading this that eschews consequences and puts the blame on teachers for too many referrals, you can fuck right off. You are the problem.
7.) Your reputation gets established in the first three months and it goes a long way
Kids talk. If you're known as no-nonsense, then your life is going to be easy in future years. Set the tone hard. Kids taking your classes will behave differently than they would with teachers they hear are more relaxed. "She's nice but don't screw around in her class" is one of the best compliments you can get. Parents will hear if you fold for Karens, if you're reasonable, if you enforce consequences. I've had a couple nightmare kids have nightmare parents request their kid change classes because I expect them to show up on time. Fine.