POSITIVE SELF TALK
When your child does something positive, give him a specific complimentary adjective. This is different from saying "good boy".
Why not say "good boy"? Say you ask your child to clean his room. You walk in and the floor is clean and it seems everything is picked up. So you say, "You cleaned your room. Good boy".
Let us say the child really did clean up everything. The next time you ask him to clean up his room, he doesn't. Last time, you said "good boy". This time what is he thinking? Is he thinking he is a bad boy? The reality is that he is not intrinsically bad. Most of us have a messy garage or office but it would be ridiculous to assume we were bad people because of that. The second problem with saying "good boy" is that he might have stuffed a few things under the bed or in the back of the closet. If this is the case, the child knows the word good does not apply to this situation and that he is being falsely praised.
Try this instead. You walk in the room after you have asked him to clean his room and you are guessing that there are a few things stuffed under the bed. But you do notice he put the books that were on the floor on the book shelf and he hung up one shirt. You say, "I see the books back on the book shelf and the blue shirt hanging in the closet. That is what I call organization." He exercised the quality of organization with the books and the shirt. He can take this success in organization and build on it.
Other specific compliments:
"You picked up your brother's bottle. That is called being helpful."
"You waited for us to go to the park. That was very patient."
You didn't eat the cookie before lunch. You had self-control."
You can also create positive self-tapes with a question.
"You put sunscreen on at the pool, will your arms feel burned or feel good tonight?"
"You brushed your teeth. Will your teeth feel clean tonight?"
"You got in bed when I asked you. Will you get a longer story now?"
After a while, your child will start internalizing these genuine compliments and see himself in those ways. Remember, whatever you repeatedly say to a child will often become his inner voice for the rest of his life.