One of most common reasons employers cite for not hiring a qualified candidate is "unprofessional appearance." Here are six other factors that can help you remain in unemployment line: (1) Being unprepared for interview. Prepare, plan, and practice! In today's tough job market, you MUST do everything you can to give yourself an edge... preparation is key.
(2) Not being able to communicate clearly and effectively. This is important during interview and on job. Being nervous can really mess up your communication skills, so being well prepared and practicing what you're going to say are always your best bet.
(3) Being aggressive, arrogant, or acting in a superior way. No one wants to hire or work with people who think they're better than everyone else. Be careful with your attitude, even if you think you're surrounded by incompetent fools. Being confident is good. Being an arrogant jerk is bad.
(4) Making excuses for failings. Your teacher never bought "The dog ate my homework!" and your boss isn't going to buy "The finance department gave me wrong figures!" In grown-up world, you have to take responsibility for what you are responsible for! You'll never earn respect by blaming others when things go wrong.