Know what you want it to look like. Choose and use positive language that clearly and unambiguously describes your behavioural expectations — and use the same language consistently. If you don't know how you want behaviour to look, you can guarantee students won't either.
Teach your expectations. When you know exactly what you want behaviour to look like, make sure students know too. Taking the time to do this pays dividends throughout the rest of the year.
Have a planned system for recognition and consequences. Put consequences in a hierarchy and make them easy to implement (otherwise you won't use them) and make them as immediate as possible. For recognition, put your emphasis on class-wide rewards.
Use class-wide rewards. It is not fair to give Johnny a reward for not throwing chairs, so it is much better to set up a system where everyone benefits when he makes the right choice. This way the class support the challenging child instead of resenting them. Arrange in private, announce in public.
Act calmly and confidently in charge — even when you're not. You will always be more confident if you have a plan. You are just delivering a system.
Take the time to get behaviour right. Reception teachers do not start teaching reading the moment children arrive in September. They spend lots of time teaching routines — and they get that time back. You will too.
Ring home with good news first. This makes ringing home with difficult news much easier. You will already know the list of students this might apply to.
Don't counsel children just after they've made a bad choice. Some children don't mind whether your attention is positive or negative — they just want attention. Talk to children about their choices, but not immediately after a poor one.
Never shout (unless you are trying to catch the attention of someone quite far away). If we shout, we suggest that raising our voice is an appropriate way to get what we want. It is not.
Don't investigate unless it is too serious to ignore. Has anyone, in the entire history of children, ever really got to the bottom of an incident they did not see? If children tell tales, remind all children involved of a specific and relevant instruction and monitor the situation. This saves hours of time and is far more effective.