Rather than answer with a negative try a positive approach rather than just a No.
For example:
Child asks: I want a biscuit? (Just after breakfast)
Response: Of course you can have a biscuit for morning tea. If you’re still hungry we can make something/would you prefer a piece of toast, etc? (Give an alternative and change the direction of the request).
You are on your way to somewhere and are in a hurry and said child wants to balance on the wall. To hurry them along instead of saying no rephrase it to something like…perhaps another time, instead lets race to see who wins…ready, steady, go!
Or when you are at the park with your little one and it’s time to go and they say I want to play longer. Instead of just no give them another five minutes – saying “ok, you can have five more minutes”. Then give them reminders about the dwindling time such as two minutes to go, one minute to go, almost time to go after 3 more pushes on the swing. It allows them to feel you listened and they have got the more time and ideally it is a win win as then there is no power struggle as you are doing a countdown to the time to go and by telling them that there are only 3 more pushes on the swing gives them a definitive time frame and end.
Be creative with the answers rather than a straight out no.
Give explanations as sometimes there is another reason why it is not possible and then they cn see that it is not to be mean but because there is a reason.
Offer an alternative rather than just a no.
Suggest an alternative time such as …that’s a great idea; what about we do it…..
If it is at the end of something then compromise and offer a specific amount more such as one more time and then it’s time to (whatever- go, stop the activity, etc).
If it’s a food related request perhaps offer a reduce amount so that they get a little and it isn’t a bit issue. Then if they still want more then offer for alternative time and give a reason why.