With the right preparation, the informational interview is a great opportunity to get career advice, focus your job search and bolster your network. In my first experience, I found my preparation was lacking even though I'd done my homework.
The person I was meeting with immediately asked why I found that career path interesting. I explained the various aspects that were very appealing to me. At least, I thought I did, but something about the delivery led him to ask, "So this interest is fairly new?" Despite the impression that I had taken time from his busy afternoon on a whim, he graciously went on to explain things like what his office does, the typical day, and the challenges of his job. I value what I learned, but missing the initial opportunity to be taken seriously led to a less in-depth discussion than I had hoped to have. Worse, it left this contact with a lukewarm impression of me.
Here are a few tips to get the most out of an informational interview:
Communicate before and after
Don't be afraid to ask. When requesting the meeting, frame it like you would a cover letter. Err on the side of being more formal than necessary, and be brief. Don't send a full autobiography, but do include why you would value his/her advice. It can't hurt to talk about some of their achievements in your request. Send a thank-you as soon as possible afterward. Go beyond the generic thank-you note by including specific details from the meeting.
Prepare questions
Obviously, don't ask about anything you could easily look up. Do ask things like how their responsibilities break down as a percentage of their time at work, what are the best/worst things about their job, what the most important skills for that job are, etc.
Prepare to present yourself
Practice your explanations of what you do and why you are there. When the purpose of the meeting is to talk to someone about their job, it can be easy to forget that in doing this you also have to present yourself. It is crucial to the experience of effective networking and learning all you can about that person's career path.
Dress appropriately
Even for an informational interview, wear what you would to work in that person's office. You'll be more comfortable and confident if you're dressed like you might belong there.
Make sure you get to your top questions
The art of the "polite interruption" can be a very valuable skill. It's much better to look a bit overzealous than it is to seem uninterested. Don't wait for the pause in conversation long enough to say everything on your mind. Rather than trying to frame your point all at once, jump in with "About ___ you just mentioned…"
DO NOT ask for a job
Going into the meeting with one stated purpose and then revealing your goal was something else does not look good. That makes you seem disingenuous and like somebody they would not like to work with anyway. Don't do it. It's great if the interviewer recommends applying for a position. Follow up in that case, but don't bring up a job yourself.
Keep the conversation short
It is doubtful they have allotted more than 30 minutes. Don't overstay your welcome.
That being said, remember this person did agree to give you their time. They would like to help you find your way. Now make the most of it!