Informational interviews are one of the best ways to get a toehold in a new career.   First person, conversational research is always of a higher quality than the written word.  You can get a tonne of little details and insights from people in real life that a text or scripted video would never reveal.  
Informational interviews are surprisingly easy to get.  My preferred method is to log on to Linked In and search for people in your area with the job title you want.  Then I offer to take them out for lunch and ask them questions.  I find something near their office, so its easy for them to say "yes".  So far, I have about a 50% success rate.  People love to talk about themselves and what they do all day, and get very few opportunities to do so in real life.
So, what are the dos and don'ts for informational interviews?  I will start with the don'ts because they can kill your interview quickly.
  1. Don't be late.  Punctuality is a good trait in an employee and business contact.
  2. Don't ask for a job!  You are there to collect information, not ask for something.  This question puts the other person in a difficult situation.  If they want you, and have an opening, they will ask you.  
  3. Don't ask questions you could answer through your own research.  This is just rude.  Why waste their time?
  1. Do respect the other persons time.  They are helping you out, try to make it easy on them.
  2. Think of your questions in advance.  Write them down and bring the list.  Here are some example questions.  (Notice how they focus on the interviewee's personal experience and opinion.)
    • What's a typical day like?
    • What do you like the most/least about the job?
    • What do you know now that you wish you knew then?
    • What advice would you give to someone starting out in the industry?
    • If you were me, how would you get into the industry?
    • Is there anyone else I can talk to at your company?
    • Are there any books on the market I should be reading?
    • What strengths do you think are most helpful for this job?
  3. Share something about yourself.  Don't expect the interview to be a one way street.  Let the other person know something about you to make them feel at ease.
  4. Dress appropriately.  Think of it as a business meeting.  Consider at least business casual. 
  5. Be a good listener.  This entails demonstrating you have been listening.  I like to summarize what the other person has said in my own words every once in a while.
  6. Take notes.  This can be during the interview or after.  Write down what was said and your impressions.  Review your notes in a couple of days.
  7. Ask for referrals (if you've made a good impression).  Don't be shy to ask to the interviewee to introduce you to other people in the field.  
  8. Pay for lunch or coffee.  Even if you are unemployed, its a nice way to show that the other persons time and expertise is valuable to you.
  9. Say thank you.  Follow up with an email the next day.  Consider including any action steps that might have come up during the interview.  
As someone who's changed careers a couple of times, I've found informational interviews to be a great way to get into industries.  When people say "yes" to being interviewed by you, it can open up all kinds of doors.  Lots of people like to help other people succeed.  Its one of the great things about human beings.  Why not go ahead and accept the help?