Mistake #2 - Making Arbitrary Rules
The generation of students we're teaching right now is smart. And opinionated. And vocal about it. So when you decide what your official classroom rules are going to be, I recommend that you make absolutely sure you have a good reason for each one, a reason that you can defend to the death if need be and consistently enforce. Why? Because making rules that seem to have no logical reason behind them in the eyes of your students is an invitation for breaking them and getting into arguments in class. They will have a hard time buying into keeping rules that they don't view as necessary. It's simply human nature, and we teachers do it too with our administration, if we're being honest.
Examples of possibly-arbitrary rules that may be hard to defend and enforce:
1. No food or drink. I used to die on this hill, but that was before 2004ish, when there was a generation shift. Nowdays refusing to allow kids to have food and/or drinks in class is cause for all-out warfare in their eyes. In 2009, when I went back to the classroom (after working as our district's ELL coordinator for 4 years) I actually got a parent complaint that I hadn't allowed her son to drink his breakfast smoothie in class. I saw the writing on the wall. Yes, food and drink can be distracting. Yes, it spills and gets on desks. Yes, it creates trash bits on your floor. But to me, it's not worth arguing about anymore.
2. No gum. It's hard to notice that kids have gum, and therefore, you're always going to be fighting and fighting this battle. And you'll get accused of singling out and making some kids spit their gum out when others are chewing it too. And students see it as completely arbitrary, even if you argue until you're blue in the face that chewing gum hinders their ability to speak the target language, because actually, it really doesn't. You may not speak very clearly, but you technically can talk while you have gum in your mouth.
3. No cellphones in sight. Besides being completely impossible to enforce (it's like playing whack-a-mole,) this rule wears me out due to the arguing and haranguing I feel I have to do in order to have some semblance of control over whether their cell phone is "in sight" or not.
4. No talking. The generation we're teaching right now is very verbal. You'll have kids in class that literally talk themselves through just about everything they do, because that's how they process. In my class, there's plenty of talking at various points during class. I talk to them and they talk to me, and we all talk together. But I can get them to focus and quiet down when it's necessary for learning because I'm not constantly squelching ALL talking.
5. No bathroom breaks/limiting bathroom breaks. This is another one that can get you into trouble with parents, and keeping up with limited (paper) bathroom passes and the like is just not a part-time job I'm willing to take on. So I technically allow unlimited bathroom breaks. But if a kid asks me in the middle of some part of the lesson, I ask them to wait until we're done reading, writing the essay, acting out the skit, or whatever part of the lesson we are doing--unless it's an emergency, and I make sure it's not before denying the bathroom visit. That sends the message that I expect them to participate in the lesson first, but that I understand the need to be able to go to the bathroom when necessary. I honestly don't have that many students ask during the lesson, because of how I handle it. I do also give a 4-minute classroom break in the middle of my 90-minute block, and at that time I allow five students max out of the room at a time for bathroom or water. Most students wait until then to ask, and it seems to work out really well. (Plus they get that all-important brain break, so that when we reconvene I can get another "prime time" of about 10 minutes or so of new learning. See David Sousa for a full explanation of the primacy-recency effect and prime learning times.)
Those are just a few examples. I do have a couple of arbitrary rules, but they are ones that I am willing to defend and argue about. Mine are:
1. No sitting on top of desks. Once the bell rings, if anyone was sitting on top of a desk, they have to sit down in their desks. I don't know why, but I find this rule (which you could argue is kind of arbitrary) fairly argument-free in class.
2. No trash on the floor. This one is arbitrary and I admit it the first day of class when we go over my syllabus. I tell them, "You know how every teacher has their 'things,' well, this is my thing. It drives me crazy to have a messy floor because I live in this room all day and I don't like living in a trash heap." My floor isn't always spotless, but having this rule in the syllabus and talking about it does reduce the amount of trash left behind throughout the year, and it makes me feel less like a horrible nag when I ask a kid to pick up the little bits of trash around his or her desk before they leave.
So I'm not saying you can't have some arbitrary rules, but I would recommend keeping them to a minimum and thinking them completely through before you decide to put them out there. If you don't consistently enforce your rules, your students won't take you as seriously, so I personally avoid having rules that I know will be hard for me to enforce.
So that's it! Happy rules-making.