You should be warned: this is not going to be another exhaustive list of all the questions you can ask in an informational interview. I assume you already know why informational interviews should be part of your career journey. If you don't, here's the short of it: talking to people about their careers is WAY more helpful than guessing what a company, job, field is like to work in. I'm here to talk to you about the stuff people don't prepare you for. These are the things that if you don't follow, will drive your interviewees CRAZY and will pretty much guarantee this will be the last professional conversation you have with them.
Know who you are
An HR professional recently told me about a request she got from a young professional for an informational interview. When the young man arrived, the professional asked where her "interviewer" was hoping to go with his career. The interviewer was stumped. He had no idea. And worse - he started asking the professional to guide the question-asking! Please don't be this guy. Have enough self-awareness to be able to articulate your interests and goals and how these line up with the person you're talking to. This will ensure you can lead the conversation and will help your interviewee understand how they can help you.
Get specific about the purpose
Clearly state in your email or phone call WHY you want to talk to the person of interest. Just like applying for a job, it's good practice to let them know how you heard about them and why you're reaching out to them specifically. Be sure to also add in what you hope to gain from the informational interview: more insight into the industry, advice for someone breaking into the profession, or even to hear more about their own professional journey. End with an estimate of how much time you expect it to take (not longer than an hour in most cases) and whether you hope to conduct the conversation on the phone or in person. Bonus points for proposing 3-5 days/times you're available for this interaction.
Guide the conversation
Have a list of questions prepared beforehand. Make sure these questions are tailored to the person you are speaking to. The BEST way to do this is by googling your interviewee. Take note of their professional experiences and accomplishments. Know where they went to school and what they majored in. You can use this information to pull richer content out of this experience. For instance, instead of asking, "What jobs or experiences led you to this position?" you could ask, "I know that you previously worked in real estate. How did you make the transition to government contracting?" You'll also score bonus points for doing your homework :)
Do not ask for a job
Reminder: this is not a job interview. The purpose of informational interviewing is to access information that will help spur your career decisions. In rare cases you may have great rapport with your interviewee and they may know of a job opening. Don't count on it. You should actually be conducting these conversations well before you're in the thick of your job search. Feel free to ask if you can stay in touch, and even follow up with a LinkedIn connection request. Looking at this experience for something it's not will only prevent you from creating a genuine connection and taking in the advice your interviewer is sharing.
Follow up with a thank-you note
I just wrote about the importance of thank-you notes. The lack of one will be noticed. On the flip side, I can tell you receiving one will make you stand out. Unfortunately too many young professionals do not take the time to express sincere thanks to those who help them along. Time is money, honey. And if you're not recognizing the value of someone's time, you can guarantee they won't be there to call on when you're looking for a job.
I want to hear from those who have been contacted for an informational interview request. What made these people stand out, in good or bad ways?