Here are some things that all the parents use wrong without even knowing.
Here are some tips and alternatives to "NO" and start using these alternatives phrases. 

Alternatives to "NO" and Negative Parenting Language

"Stop hitting" Instead of this phrase use this.. "Please keep your hands to yourself"

"Don't say that" Instead of this phrase use this.. "Please choose another word"

"Quit whining and crying" Instead of this phrase use this.. "Please use your words"

"I can't hear you" Instead of this phrase use this.. "Please speak louder/more clearly"

"I won't buy you that" Instead of this phrase use this.. "Instead of that, what if we______"

"Don't get upset" Instead of this phrase use this.. "Its's okay to feel that way, but_____"

"That's not for you" Instead of this phrase use this.. "That's _____'s, can I offer you_____?"

"We can't play"/'Have to stop playing" Instead of this phrase us this.. "May be we can play later after_____"/"We have to go"