Definitely start the lesson with a big smile and with an easy starter activity. If you are running between building make sure the starter is printed on paper so they can get started straight away while your sort out computer and register etc.
Priase, praise and more praise. I always have star of the lesson at the end of the lesson and email form tutor. In fact get form tutors and parents involved early for positives as well as negatives.
Make sure they know behaviour and consequences, both positive and negatives, are their choice.
If a child is playing up say 'Daniel last lesson you put lots of effort into your work and you were fantastic. Lets see if you can do it again.' If they are starting to misbehave at the end of the lesson say 'Daniel you have been fantastic so far this lesson and we only have 10 minutes left so don't spoil it now.' Make sure praise is specific so rather than 'well done Daniel, you say 'Daniel well done for showing good listening.' Try to start with a students name so they are listening.
Make sure rules and expectations are explicit. When you explain a task also explain the behaviour expectations or ask the students eg 'When we are listening to people's presentations how do we need to behaviour?'
Circulate the room and verbal check in with students, ask across the classroom the the student your now is making good progress 'what question are you up to Katie?' Excellent well done and then the same to another stundet. It is very helpful to ask the student next to the one that has just come off task as it prompts them to get back to work.
Make sure you have a seating plan and for more difficult classes change it every 6 lessons as it is a clear message that teacher is in charge.
At the end of the lesson when you review learning objectives review the behaviour of the class and make sure you share this with them.
If they argue use partial agreement. 'Jack you may I have been talking about the topic but I said very clearly that I needed everybody to listen to the instructions. You choose to talk so you choose a C1'.
Most of the time you don't need to be confrontation but and you just need to redirect them them back to their work. If they are messing around with their planner or something I would say 'that planner seems to be getting you into trouble why don't you put in your bag out the way.'
In most classes you will have a few very challenging students(get them on subject report or whatever your school uses), a few amazing students and the the middle ground who can go either way. It is middle students who you need to work on.
Startegies that work are not out dated but speaking for myself I often forget about things that do work.