1. Forget who is asking whom for a favor. When someone asks to meet with me, s/he is asking for a favor of my time and my experience. All interactions should be taken in this light. This means you should not expect the interviewer to do the majority of the work setting up the appointment, ask me to make long distance calls to set up an appointment, or frankly do any work that the interviewer doesn't offer to do.
2. Ignore explicit instructions or direct questions when preparing for the interview. I requested specific information on her career goals and experience before the interview, so that I could see if anyone else was interested in meeting with the job hunter. I received no reply. I also received a copy of her resume the day of the meeting - when she could have emailed it to me a week earlier, when I asked for it. I had given clear instructions about how to enter my building which she ignored (we have two entrances, and going to the wrong one is actually a bit of a hike for me). While none of these amount to a major sin, she lost a great opportunity to meet others at my company, and she showed that she cannot follow directions.
3. Have vague or meaningless statements related to your goals. Are you looking for a job in this industry? A related one? A research job, a project management job, a sales job? Be specific.
4. Fail to do your homework - and worse, lie about it. I had sent the job hunter some information on the project and group I work with. When we met, she said she had reviewed it - however, a cursory conversation revealed that either she had not read it at all, or she had and seriously misinterpreted what she had read (and I am not sure which is worse).
5. Fail to ask any questions. What struck me halfway through the interview was that she had no prepared questions for me. In fact, at the end of it, I really got the feeling that she didn't see that SHE WAS SUPPOSED TO INTERVIEW ME, not the other way around.
6. Forget who is the expert. I expect that young people will have the arrogance of youth - they don't know enough to know that they don't know enough. However, I never expected to have a recent college grad, with no work experience at all, offer to make industry connections for me. When she was busy not asking me questions, she was telling me about the industry - not sharing experiences, but telling me how it works, and offering to share her contacts. And she got it wrong.
7. Fail to listen. When I managed to get control of the interview, I decided to tell her some things I tell all folks interested in this industry about the educational and work experience requirements, which she blew off.
8. Insult the interviewee by overestimating your abilities. At the end of the interview, I asked her again what sort of position she was looking for right now, and she said "Managerial position, with an assistant." I replied, "I have ten years of experience and a Master's and I am at a manager's level. I don't have an personal assistant. Our team assistant has five years more experience than you. No one in this field gets that sort of position straight out of college." She said, "Oh, but I know that I can get that sort of job."
9. Ignore time constraints. I had told her from the beginning that I had one hour. Towards the end of that hour, I said, I have to go now, I have another meeting. She ignored me. I finally had to start walking to the exit, forcing her to follow me.
10. Fail to send a thank you note. It is just polite to send a thank you note when someone does you a favor, and it also allows you to follow up with any subsequent comments or questions you forgot to ask. I am still waiting for mine.
Take a look at this first-person account of a top ten list of things NOT to do in an informational interview.