The training process should involve being conscious of your gestures. While the body movements of any person happens on the unconscious level you can easily keep them under monitor by paying attention to any changes that happen in your posture.
In the beginning you will find it difficult to keep up with every move you do but as the time passes you will get used to noticing these changes.
Once you start noticing these bad gestures bring your body back to the relaxed state. As the time passes you will be able to prevent yourself from taking such gestures whenever needed.
Your body language can control the impression people form of you.