Day one at school is the typical 'rules' day - writing the list of rules that students contribute to and then the list goes up on the wall. For the last few years, I have abandoned the 'rules' for a system that I think works much better.
Day one in my classroom goes like this: we collaboratively create a y-chart of a happy classroom (what it looks like, sounds like and feels like). We then come up with a few sentences, summarising our top ideas. The next step is considering the vocab - we improve our sentences with better word choices. These sentences then become our 'Class Pledge', which is displayed in the classroom.
This class pledge is incorporated into our morning routine. When we come into the classroom, students will sit on the floor space. I say good morning and the students say good morning back to me. They then launch into saying the class pledge together. It has taken my class this year one week to learn the pledge by heart. I started by displaying it on the Smart Board for students to read each morning and become familiar with it, but the class is now ready to say it independently without the visual reminder. It's always a lovely moment, that first time they say it on their own - so proud!
If a student misbehaves or is off track, I always refer back to the pledge. Eg. "you promised that you were going to be determined in your attitude. I don't see that right now. How can we change that..."