Never speak ill about your last company or manager. Your last job could have been an exercise in futility or your boss was not accommodative but expressing these reasons immediately will put you in a wrong position. This could make an interviewer suspicious about your state of mind and candidature. Offer just those things which will help them in one way or the other in the association.
In case the interviewer asks you directly that were you anxious about the interview or present circumstances then never say you were nervous and off course never show it during course of interview. Try not to discuss a restless night or whatever else. Be certain and confident during interview.
Never exhibit that you are so much desperate to get a job. Showing your desperation during interview for getting job would create a negative impression on interviewers mind. It might be your first job interview or maybe you have not quite got the an appropriate job till now in either case maintain your composure and keep the discussion on your strengths and skills related to the job.
Do not bring your personal issues into discussion with interviewer. Bringing up such issues would make the interviewer to feel that you will be excessively occupied with individual stuff and won't have the capacity to work with focus. Leave those issues aside and discuss the certainties that place you in a beneficial position.
Do not ask unreasonable questions like what perks will you get? How often do you guys give promotions? How much will be my salary? How much vacation time do I get?