Hands down the most important tip. Kids need to understand that their actions have consequences.The severity of those consequences will vary from child to child depending on how they react and of course the significance of the initial behaviour. With Little E the consequence have to be meteoric as she simply doesn't react to toys being confiscated, the threat of missed after school clubs or the loss of CBeebies. Most recently she isn't taking part in the local carnival parade after an incident at school. Which breaks my heart to enforce but it is the only thing I know she will actually respond to and understand as a punishment.
If I reacted to everything Little E did we would never leave the house, I'd be living under my duvet in the foetal position. So to keep the household functioning I have an imaginary line, it is pink and fluffy, and any negative behaviour creeping towards the line I ignore or I do everything I can to diffuse without a confrontation. Once she steps over the line then I bring out the big guns and consequences arrive (see above).
Kids constantly push the boundaries to find the limits. If you chop and change your reactions then they have no idea what is and isn't acceptable behaviour. So keep those goal posts firmly fixed and to avoid 'but Dad/Nan/Grandad etc say it is OK' make sure others in your family or childcare setup understand what the rules are and keep the consistency (Good luck with explaining that to your Mother in Law).
Once they break you they have won and your authority goes down the toilet. Even if you feel like your brain has turned to jelly and you can't possibly handle one more tantrum in the Tesco's bread aisle because you won't let your child eat yogurt in the trolley without a spoon, you simply have to. You are the boss. If you back down you lose. Full stop. When you are dealing with a child with the will of steel you need to draw on everything you have. And if you haven't got it then fake it, you can always cry under the duvet later when they can't see.
This is for those of you who've been screaming 'REWARD CHART!!!' throughout the post. Sticker or tick based reward charts can be amazing at motivating children to behave well. Lots of kids don't need more than the simple act of filling in their chart, whilst some need rewards at the end of the day/week when their chart is complete. But before you all clamber onto Amazon and pin your hopes on the £20 magnetic rocket shape chart, it doesn't work for all kids. Little E is of course one of those children. She needs instant gratification for her behaviour. I've tried every kind of chart under the sun and within 48hrs it is old news and she really couldn't care less if the pony makes it to the stable by the end of the day. So we have reverted to simple praise when she does something positive. It may be a thumbs up or a hug for little things like helping her sister or cleaning her teeth nicely and we have a jar full of small treats for when exceptionally good behaviour needs to be rewarded immediately. I just need to find somewhere to hide the jar...