Just Another Geek and Zsofia have provided good answers. I think education classes can be of value… but there is nothing like being in the trenches putting theory into practice. I taught in an inner-city elementary school in Houston for several years and went from being a possible hiring mistake to one of the best classroom managers in the school so I can certainly relate to the OP.
Deep down, kids hate chaos. They want order and predictability (to an extent). New teachers are in a chaotic state, which is at odds with what students need (but rarely say they actually want). Teachers have to be able to quickly deal with distractions by thinking out every possible interruption (bathroom breaks, kids without pencils, smart-assed comments) and having an immediate, yet not distracting response. And I mean for everything. If kids notice a tendency for a teacher not to respond to certain behavior… guess what, they’re going to do that thing, whether it’s whispering, getting up without permission, speaking without being recognized…
I was a horrible classroom manager when I first walked into my fourth-grade classroom… the kids fought, talked back, you name it - they did it. I kind of had to bottom out (having two boys brawl in my classroom when I left for less than a minute to deliver my roll card as an assistant principal walked down the hall pretty much did it for me!). I learned to be consistent and to always have a response - even if it was just a look saying “I saw what you did, and I don’t approve!”
Responsibility is key. In my classroom, virtually every kid had a job, from passing out papers, to monitoring the line, to holding my keys when we were at lunch. They loved it and they also knew that bad behavior was the one way of losing their job… so they tried very hard to do the right thing. I saw some of the most beligerent kids walk off insults and make great choices because they didn’t want to go through the humiliation of being “fired.” I also had a great system of rewards and consequences - the home visit. Since I taught at a school where every kid lived within a mile and a half of the school, I made it clear that I would be in the neighborhood EVERY DAY after school. Initially I thought about home visits as a punitive measure but the kids absolutely loved for me to come by and tell their mom or grandma that they had a good day, or were doing well in class. The parents appreciated it too. Too often the only contact they had with the school was for negative stuff (kid gets in trouble, parents get called in). What a surprise to get a call or a visit because you’ve done a good job teaching your kids manners and respect!
You can’t be someone else, or adopt a persona that you’ve seen someone else use. It has to come natural. If you deal with problems with humor, you should do the same as a teacher. If you’re able to come up with witty comebacks to the kids you should do that. If you’re kind of square and nerdy, be square and nerdy - the kids will respect you for being real. If you’re phony, no matter how cool you appear, the kids will have no respect for you.
You have to have enthusiasm and a fun attitude about your subject(s). Doesn’t mean you have to blow up stuff in class every day, or walk around grinning if that’s not your style, but you have to see the value in what you’re teaching and encourage that for the kids. When we had math class I worked really hard to make the abstract concepts concrete and real, even if the best reason I could come up with was “Well, you need to know how to add fractions because you’ll be doing it in fifth grade.”
Last, as has been said, you have to give a damn about the kids you teach and the community in which you teach. If you don’t care they won’t either.