A classroom management plan is your answer to one question: how does this room run? It covers what students do, what you do, and what happens when things go right or wrong.
Many schools require one. Even if yours doesn't, writing it down forces you to make decisions before a student forces you to make them on the spot.
Keep it to one page
If it doesn't fit on one page, it's too complicated for students to follow. Write it in the order students experience the day.
What goes in it
1. Expectations. Three to five, stated positively. "Be on time and ready" instead of "Don't be late."
2. Entry routine. What students do the moment they walk in. (Most teachers use a daily bell ringer.)
3. Attention signal. How you get the room quiet, every time.
4. Procedures. Materials, bathroom, turning in work, late work, devices, transitions.
5. Recognition. How students who meet expectations get noticed.
6. Consequences. Small, predictable steps, from a reminder up to administrator involvement.
7. Family contact. When and how you reach out, good news and bad.
8. Exit routine. How class ends. (An exit ticket works well here.)
Teach it, don't just post it
Spend the first days teaching and practicing each piece. Revisit it after long breaks. A plan students have never practiced is just a poster.