Even small signs should be paid attention to. A slight biting of lips, or wetting your lips with your tongue or even shoulder shrugging should be kept in check. Analyse your usual body language and practise changes before you attend the interview.
Badmouth your old Boss / job:
Maybe you had a boss à la Devil Wears Prada, but your hiring manager doesn’t need to know that. Badmouthing your former employer just gives off negative vibes and detracts from your professionalism