At some point, all children pass through phases involving habits that annoy parents. It is important to break the habits that are undesirable before they become part of the permanent personality. Breaking a habit involves breaking the connection between the trigger and the resulting action. First decide whether the habit needs breaking or not. It may be something they will grow out of on their own and for the current time, supplies a need they have. A general guide might be that if the habit is causing a physical problem or in teasing from other, it needs to be broken.
The first thing to try in breaking a habit is to remove the trigger. Keeping a diary is a good way to identify the situations. Does he seem tired, bored or angry? If the trigger is part of the environment, change it if possible. Maybe there is a new teacher at school or another child is being mean that is causing the action. If the habit is a small one, it may be better to change the situation around without telling your child. Confrontation over something relatively small can make the habit into something bigger. If the habit is a big one, then the child needs to be involved if they are old enough to understand.
Since children imitate the adults, especially parents, in their lives, take a hard look at you and your spouse. Maybe your child has picked up something from yourselves and you did not even realize that you were doing it. Some children rely on a habit to comfort themselves if they are stressed. Find what is causing the stress in your child's life and try to change it.
Offering a substitute is a very effective way to deflect a habit. If the child is rolling a ball around in his hands, sucking his thumb will be out of the question. Teaching your child to use his alternative when he feels himself heading toward the habit is a great confidence booster. He has learned that he can accomplish something big. Even a competing habit can be introduced. Instead of sucking, teach your child a game that hides his thumb under his fingers or his pillow at night.
For teeth grinding, make sure the child is relaxed before bedtime. Even some minor jaw muscle massage may help or let the child feel the damage being done to his teeth. If your child is a lip biter, have him keep some chap stick on hand to use instead. Nose picking can be deflected by teaching and keeping a Kleenex handy for them. If their nose is sore, point that out.
Thumb sucking and nail biting can be helped with pointing out the bad things. Make the child aware of how the thumb being sucked is probably sore and the other thumb is not. Show a nail biter your hands or someone with nice nails and contrast that with theirs. For a girl, a manicure and some nail polish will make them want to keep their nails pretty. Hair pulling is probably related to stress. Teach them some relaxation techniques and show them the bald spots.