Just a few quick ideas.
When a student presents you with something negative, agree with them, at least in part:
''Oh Sir, it's too hot!''
''Yes, Fahim, it is. I've opened all the windows and I've said you can take your blazers off if you want; but there's little else I can think of to do... Can anyone think of anything else sensible we could do? And I don't mean have a pool party!"
There is a school in Rochdale which, for years, had this as its mantra for all staff. Turn a blind eye by all means, but turn too many blind eyes and you may be allowing the culture of the school or of your class to change
If you allow a student to 'get away with' a behaviour once you are effectively condoning it. If it's behaviour you don't want to see again, deal with it.
Too often we skip the 'think' stage, which means we just feel, then react (in life as well as in the classroom). Good behaviour management is all about thinking about behaviours rather than simply acting on them on the basis of something we were made to feel.
How often do we, in our personal lives, feel something that has no bearing on reality? (S/He didn't phone so I must be not worth phoning?) Use your brain to engage intellectually with the situation, and to think about how you might act.
Not so easy in the penultimate week of term and the one nerve you have left is under attack!
"Sadie, I need you to turn around and focus on your work, thanks." Then when she is just on the cusp of doing what you say...
"That's great, the right choice!"
Try to avoid waiting for the student to make the change you've asked for. Make your request, firmly, then avert your attention, at least partially, until the student complies. Then praise them, perhaps noisily, perhaps quietly, or even silently (depending on who it is).
For example, Daniel is a cool, sporty student who is a strong personality and has the respect of his peers: "Daniel, you have a pen, you understand the task, you've already told me you don't have any questions, so there is nothing keeping you from working. I want to see you working, thanks." (Walk away or look away; as soon as Daniel begins to work, walk by him and quietly praise him; quietly, so as not to embarrass him.)
Try this as a test. Say to your class when they are a bit rowdy: "you're behaving like animals in a zoo!"; then at another time try "now then ladies and gentlemen, how do we think we should be behaving in this room?" If you give them the idea of behaving like animals in a zoo, there will generally be one or two students (at least) who are keen to show you what a zoo animal really looks like!
Make a set number of positive phone calls home every Friday. Know that before you go home you will contact (either by email or phone call) four parents every week. Make sure you don't ignore those quiet students who work solidly all day every day - it's a great way for them to feel noticed in a system which often rewards the usually-noisy-occasionally-silent students.
The classroom management / behaviour guru, Bill Rogers, talks about the fair certainty of the consequence, not the severity of the consequence, being most effective when dealing with behaviour. See more of Bill Rogers' ideas.
Bill Rogers talks of tactically ignoring the secondary behaviours, and keeping the focus on the primary issue - the one you are dealing with at that time. He tells a story in his book, Classroom Behaviour, about dealing with a girl who threw an eraser across the room. He calls her over, several times...
"She came over and stood next to me, with folded arms, averted eye contact, eyes raised to the ceiling and sighing ... 'What do you want?' she said, in a careworn voice.
It's hard to keep the focus on the 'primary' issue or behviour. Tactically ignoring the sulky non-verbals... [but by doing so] we avoid over-servicing the student's goal of attention or power."
If you are able to get a copy of any of Bill Rogers' books (and you can get old editions on Ebay very cheaply) you will see he points out that there is some secondary behaviour we shouldn't ignore, such as swearing or dangerous behaviour.
Try as hard as you can to resist the urge to need the last word. It is not 'giving in' and it is not a weakness, rather it is like walking away from a fight you never even wanted in the first place. Moving on gives you dignity, engaging in the fight loses you that dignity. Who was it that said, "if you argue with a child, you will sound like a child."