As a member of the Standing Committee on Teaching for the Association for Education in Journalism and Mass Communication, I got to particpate in "The Doctors Are In," a speed-dating session where professors visit tables for 15 minutes at a stretch to talk about teaching. My table focused on classroom management, and here are some of the things I talked about with the various groups who stopped by.
1. You are in charge of your classroom. Not because you're some authoritarian figure who wants to dominate college kids, but because it's your responsbility to provide a good learning environment for your students.
2. The syllabus is key. You have to decide in advance what kind of classroom you want to have. In your syllabus, you can describe (in positive terms) what kind of classroom environment you expect to have. It's up to you what to include here, but it might be things like "everyone has prepared for class by completing assignments" or "students regularly participate in discussions." You can comment on attendance, devices, or whatever's important to you. It's important to note that not everyone's ideal classroom is the same. I'm perfectly okay with students using phones and laptops, but not everyone feels that way. It will also vary by the type of class (for example, a lab vs. a lecture vs. a discussion class).
3. You then need to provide specific consequences for noncompliance. For instance, if students don't participate, you can threaten to administer quizzes which will be worth a certain percentage of final grades. Michelle Ewing of Kent offered the interesting idea of having "community points," so if she sees a student using a phone (laptops are allowed) the entire class loses a community point -- using peer pressure for the common good. At any rate, if you don't offer a specific consequence there's no point in describing your ideal classroom. Make sure the plan is actually enforceable and that you're willing to do what you say you're going to do (don't threaten quizzes if you don't have the time to write, administer and grade them).
4. If (when) noncompliance occurs, you have to enforce your rules. Sometimes it needs to be handled right on the spot -- one professor told me about a student who refused to hand over her phone, and another had to confront a student having a meltdown in front of the entire class. These problems must be dealt with immediately by asking the student to leave or to talk with them in the hall -- they are creating an environment where other students can't learn.
5. Other problems can be addressed later. For instance, there's the "Hermione Granger" problem when you have a student who raises her hand every single time, and everyone else groans or rolls their eyes. There is no need for this type of problem to be addressed immediately, but because it disturbs the learning environment it does have to be addressed. Asking the student to stop by your office and then explaining that you appreciate their enthusiasm but need to allow others to participate addresses the problem without embarrassing the student.
We talked about a lot of other problems, too, but those are the main points I recall. I hope I thanked everyone who stopped by and shared problems and solutions -- everyone from grad students to senior faculty contributed, which meant that I got to learn a lot, too.