Don't think of yellow. Hard, isn't it? To not think of yellow, the best strategy is to think of a different colour. So if I really wanted you to stop thinking of yellow, I would ask you to think of green instead.
So why do so many adults use the first method when giving children instructions?
"Don't run!" — when "Walk" would do the job better.
This is especially true with young children. Saying "Don't throw your food on the floor" is even less effective with little ones. I am not sure they fully grasp the negative contraction. All they hear is "…throw your food on the floor." A much better phrase: "Keep your food on the tray."
Using positive language alone does not make children behave. But framing instructions to describe what you want is undeniably more effective than describing what you do not want.
When we give instructions positively, we present an image of success in the child's mind. We are sharing a plan. We are describing the future as we would like it to look — not the present scenario we want to change.
Now, I apologise in advance. Every time you hear yourself, a partner, a fellow teacher, or anyone else use negative language, you will notice it. I have just programmed your reticular activating system — the same part of your brain that listens out for your name at a party or your flight number at the airport. You won't be able to stop noticing. Sorry.
The good news: if I have failed to programme it, you won't remember that I failed. So I can't lose.