Your body language tells a lot about you in an interview. Sit up straight. Lean slightly forward in your chair. Keep eye contact with your interviewer as much as possible (especially be aware of this when you are the one speaking as many people make eye contact when listening but not when speaking). Stay alert. When you go through a long interview process, you can sometimes start to show weariness, and startups often have a high energy culture. Make sure you project energy and do not appear tired. Try to mirror your interviewer's demeanor and style. Be yourself, but let them set the tone of the interview and match their energy level and body language. Never swear or use casual words like "yeah" and "uh-huh". Even if your interviewer swears and speaks casually.
Bring a notepad or portfolio and a pen to take notes during each interview. This is a very effective way to show your interest in the opportunity and your attention to detail.
Biggest challenges? Where can I contribute?
Ask each interviewer what the biggest challenges of the position are at the beginning of the interview. Write down what they tell you and focus on how you can overcome those challenges with your skills and background during each interview. This question basically gets the interviewer to tell you what their hot buttons are, and each person will have different hot buttons for the same position. Also, focus on how you can help them, not on what the company has to offer you. Where can you contribute to their company, team or project?
Forbidden topics - money, benefits, office tour, overtime
Never bring up money on your first interview. If they ask what you're making, be honest but tell them that you feel it's probably premature to talk money at this point and, besides, you're interested in evaluating the entire opportunity rather than the salary alone. Let them know that you're confident that you both can work out a fair offer if you are both interested in moving forward. Don't ask about benefits info or to take an office tour. Those things will come at a later time. And never ever ever bring up overtime. Even in a positive way. The interviewer will almost always remember that overtime was discussed during the interview, and they will perceive it negatively, regardless of how you positioned it. If you want to express that you work hard and long hours, let them know that you do whatever it takes to get the job done and that you are quite familiar with startup culture and expectations.
Want, not Need
Companies don't like to hire people who seem desperate. Interview with a confident style that shows you want the job, but don't give the impression that you need the job. Even if you desperately need the job. If you have been out of work for awhile and have been getting a lot rejections, inevitably an interviewer will ask you what your interviewing experience has been the past few months. Let them know you are having a very positive experience evaluating companies and opportunities. Tell them you are being selective in your interviewing process to find the right opportunity for yourself.
Laid off or Fired
It is always awkward to let an interviewer know why you left your last job if you were laid off or especially if you were terminated for cause. Never lie when asked. While it might be unfair, many hiring managers assume the poorest performers are cut when layoffs occur. Be prepared to answer your layoff question with information that will dispel any assumption someone might have about cutting the poor performers. Try to show that there was a specific business reason behind your layoff. Your department was eliminated. The office was moved. The product you supported was being discontinued, etc.
Being terminated for cause is always difficult to answer. Never use the word "fired" when describing your situation and instead use a softer term like "let go". Do not go into great detail about the circumstances and do not express anger, blame, or a grudge. Speak with confidence when discussing the situation and do not appear meek or apologetic. Look the person in the eye the entire time you are discussing what happened. If possible, offer a reference at the company who will give you a solid reference about performance. If you can't get a reference at the company that terminated you, find a reference at a previous company that will give a reference to help show you are a solid performer and offer up that information at the time of discussing your termination with the interviewer. If you show that you are uncomfortable and lack confidence when discussing this subject, you will give an interviewer the impression that there is little doubt the last company made the right decision.