Whatever system you put in place, you must be consistent in its use. Otherwise the children won’t believe that you will follow through with any consequences/punishment and the whole thing falls apart. Make sure that every student understands the class rules and knows what the consequences are for not following them. They need to know your expectations up front.
I remember one that I learned about a hundred years ago. If a student is disruptive or breaks a rule, you write their name on the board. No discussion, it just goes on the board and they can see it. (And no, “You don’t want your name on the board, do you?” nonsense. They do something wrong, their name goes up.) That’s the warning. If it happens again, with the same student, a check mark goes up next to their name. They lose half of their recess. Once more is a second check mark and they lose their whole recess. A third check mark means a note home to the parents. You can modify what they lose at each check mark to fit your situation. Or, make check #1 loss of the whole recess and #2 a note home. If the incident happens after that day’s recess, they lose tomorrow’s recess. However, all names come off the board at the end of the day and everyone starts with a new slate the next morning. You just have to note the lost recess elsewhere.
The more important, and usually more effective thing is having a positive reinforcement piece. One thing to try uses beans, marbles or beads. Each student has a container. Throughout the day, you watch for and reward good behavior. “I like the way so-and-so is working quietly, ” or whatever behavior you’re trying to encourage. Put a marble in that student’s container. Do this with many students throughout the day. At the end of the day, everyone puts their marbles into a group container. As well, if you see good behavior throughout the room, you can put a few marbles into the group container. When the container is full, the teacher springs for a pizza party, or ice cream for everyone. Something fun that the students can earn with good behavior. If you find that this is too many marbles or beans to buy, find a way to track them on a chart that’s visible to everyone. Children need to see that they’re making progress towards a goal. (This is also a good “anti-instant gratification” lesson.) It doesn’t have to be beans, it can be stickers on a chart or even just filling in squares. Make good behavior both an individual and group effort. I found that the positive reinforcement made a bigger dent than the punishment piece did.