It is worth getting behaviour management right from the start. Of course, you won't. No one does. As a new teacher, I was utterly useless and had to be bailed out constantly. I went through the predictable cycle of foot-stamping, screaming, threatening, intimidating and bullying to get control. None of it worked for more than a heartbeat.
In the toughest environments it can take a year before you can manage behaviour without sanctions or call-outs. Expect it to take time. You won't crack it in a week, or even a month. I know that this doesn't help you today, but in your second year of teaching in the same school it gets a lot easier. Children realise that you are not going away and they have new teachers to mess with. Relationships have grown, trust has been formed and some sweet memories can be fondly recalled: "Aw, Sir, do you remember when Jade threw that bin at you and Mr Jones had to hose you down? Dat was well funny."
Don't start with the "rules lesson". The children will think you are a prig and ignore you. It will not do anything to improve their behaviour or their respect for you. It will not inspire them, engage them or interest them. You can agree routines as you go along. Please, I beg you, don't "tell them how it is going to be" before you have shown them something of who you are.
Instead of lecturing them like Captain Mainwaring, do something that makes them go "Whoa!" Take a risk. Surprise them. Delight them. You will make it easier for them to openly respect you and accelerate your position in the hierarchy of new teachers to: "No, leave him out, he's all right, he lets us blow things up in science 'n that."
I remember earnestly counselling a student teacher to prepare for open warfare with my newly tamed Year 9 class. In two minutes he had shown them two magic tricks that made them go "Whoa!" and they were eating out of his hand. Of course, it may go disastrously wrong, but as the laughter dies down they will still respect you for trying. They will still set you apart from teachers who are the rule-mongers.
Plan lessons that do not require the whole class to sustain its attention for long periods. Plan activities where pupils follow pre-prepared instructions in small groups. Get them used to listening to you in small groups, and in time holding their attention as a class will be easier.
Learn names, and learn them quickly. Make sure the phrase "I'm not very good at names" never passes your lips. Be good at names. Show you are good at learning. Make your pupils feel important and valued.
Build your use of positive reinforcement gradually. Heavy reward will appear insincere until pupils get to know you. Leave your first use of positive notes until week four, then notice pupils who are doing the right thing first, every time. Reward behaviour that is over and above expectations.
Beat them into shape with respect and kindness. Refuse to deal with poor behaviour in public. Take children aside to admonish them. Establish a tally of class rewards, a team ethos, everyone working collaboratively for a common goal. When children run away, follow it up. When children ignore you, persist. When they swear, attack or abuse you, don't give them the thrill of your emotional eruption. Save your emotion for the children who are doing the right thing.
For the trickiest children, couple your finest poker face with the dullest procedural options: "This is the third time I have had to take you aside. I can see how my name might be funny ..." Step them calmly through choices and sanctions.
Take time to repair relationships, redraw boundaries and reinforce expectations with the most difficult customers. Even though you are paddling frantically under the surface and inside your head you are screaming "What do I do?" over and over, you must hide it. You must control your performance.
You are not going to do any of this alone. You need a couple of big hitters on the staff to back you up and underline expectations for those who need it. Identify these people early. Choose them carefully. You are not looking for the shouters and bawlers, the excluders or sergeant majors. Look for adults with great relationships, the ones whom children never try to confront. Seek them out, ask for their help, ask them to be a behaviour mentor (irresistible!).
The children will test you out. They are watching for your reaction. You need a carefully controlled performance that is consistent and reliable. You cannot afford to show the extremes of your range. Your fury won't help. Neither will your compulsion to grab your car keys and make a break for home in a blur of tears. "Aw, Miss, 'member when you blubbed like a 'lympic medallist ..." Keep calm, breathe.
Good luck. Oh, and know where your keys are, at all times.
Paul Dix is touring UK schools with his behaviour Inset, keynotes and one-man show The Behaviour Show. His new showreel is here: www.pivotaleducation.comkeynotes-2 Twitter: @PivotalPaul.