Many habits are performed unconsciously and may even be considered trivial- by those who do not suffer from the habit.
A common example is nail biting which can be treated by a technique known as reverse suggestion. Thumb sucking can be a comparable habit that can be dealt with similarly.
Teeth grinding (bruxism) is another unconscious habit which can have dire physical consequences, including jaw fractures.
Associated with high stress levels, it is usually treated by using direct suggestion. Cognitive behavioural approaches also have very successful results for treating unwanted habits.