The other girls have summed it up and given some great suggestions.
I will just add that my son has some hearing dificulties and it was really beginning to impact on his behaviour. He still has tendencies towards naughiness out of frustration.
What eventually worked for us, like the others have said, was absolute and utter consistancy between me and my
DH. And also we used his "currency" which is music CD's in his bedroom, and Wiggles DVD's, and his books. If he misbehaved, straight away, I would turn off the DVD/or move his CD player out of his bedroom to the garage or remove his books from his bookshelf. VERY quickly, he "got" that the boundry had been crossed, & we saw a massive improvement really quickly. (It wasn;t easy, but it was quick. I felt mean and nasty, but it worked.)
HTH?