I've done my fair share of research and I've found what works for me when it comes to interviewing, to the point that I think I can offer some tips & pointers. Some of them are obvious and standard; some are personal tips that I think can have value to you. Here they are. Try 'em out.
1. Build the interview magic. Let's talk about liminal spaces. Interviews are weird. An interview is an artificial disruption of someone's life to sit with a stranger for an hour or so, talk about some aspect of their lives with an interviewer who they know little to nothing about, and whose name they've probably forgotten by the time they're answering the first question. There's an inherent, mismatched power dynamic between interviewee and interviewer. And it's weird.
Tear that down. Cut through it. Be relatable, be understanding and even forgiving, and listen. I find that I have the best interviews when it's clear that the interviewee feels that this is an opportunity to step outside their typical experiences. The interview is an odd wedge in their everyday life, so build into it the atmosphere that it's a space not for them to be grilled, but for them to unveil things about themselves outside of what they'd normally feel comfortable doing. Insight: everyone deals with problems and situations, good or bad, small or big, and nearly everyone I've interviewed has really appreciated the space where they can talk in a way that's outside of their norm. Your job and goal, in large part, is to build a little temporary atmosphere where you're two people talking. One of you two just happens to get an Amazon gift card for their time when it's over.
2. Have a clear purpose for your project. This one seems obvious, but you'd be surprised how quickly a researcher can lose sight of the real aim of the project in designing their interview questions and guide. Your goal can be as simple as "learn more about [X]," or it could be to extract a highly detailed account of an event that occurred or decision that was made. But without a goal and guiding light, you won't write a tight interview guide, you won't get the information you'd hoped for, and you'll probably feel stupid.
3. Know that people are full of shit, and know the types of questions to ask. This isn't really that sinister, but it impacts the types of questions you ask, and how you should approach each interview. This comes to the fore when you ask questions that ultimately relate to 'Why?' and 'How?'. "Why did you do that?" "Why did you choose that brand in your last purchase?" More often than not, avoid those questions. We people don't usually know consciously why we do the things that we do (insert hella psychology, neuroscience, and methods research here), but it's natural for people to justify or explain their actions after the fact. If you ask me why I did something, I'll tell you why. It just likely isn't the real answer to the underlying why, so if you're hoping to influence decision-making (as you probably are in advertising), you've gotten the wrong answer to the wrong question.
Sometimes this is okay, and it depends on the goal of your research. One of my projects in grad school studied, as a small slice, how people talked about being and becoming fans of their favorite NFL teams (and the narratives they developed). I asked 'why' and 'how' questions knowing that I wasn't getting 'the truth,' because who the hell knows the 'truth' about being a fan of the New York Giants? But I wasn't interested in 'the truth,' and I knew exactly what I was getting myself into with those questions. So avoid 'Why' and 'How' questions, unless you know what you're getting yourself into.
Part 2 of people being full of shit: Interviewees are under no real obligation to tell you their real experiences, or what they really think about a topic. Your incentive for participating doesn't unlock people's inner secrets and force them to unveil uncomfortable details. If you're interviewing me about an uncomfortable or sensitive topic, I might just feed you a narrative I'm comfortable with. Or make something up. Because who are you to make me uncomfortable, Mr. or Ms. Interviewer? This is where your skills as an interviewer come in. It's vital in your role as the interviewer to put your interviewee at ease, to be relatable, and to be someone they want to talk to for the next 45-90 minutes. Let's get to putting your interviewee at ease.
4. Be more human (write your own interview guide). Nothing is more uncomfortable than talking to a robotronic, stiff interviewer who EXUDES, "I am interviewing you right now. You are being interviewed." Find and know your voice, and develop your interview personality. If you write the questions how they feel comfortable to you - while vetting that they still get to the meat of what you want answered, with rigor - you'll be a much more comfortable, relaxed interviewer. People don't really like being interviewed, but they do like to talk. The more charming and comfortable you can come off, the more able and willing people will be to put their guard down and just talk.
5. Overshare. Nothing breaks the ice quite like oversharing. I'm not kidding. Soon you'll both be oversharing. It can be as simple as telling your interviewee about something shitty or embarrassing that happened to you on the way to the interview, or maybe you have an anecdote that can build on why your apologetic and flustered interviewee is a few minutes late. Your aim here is to be human, likeable, and relatable as soon as you can. You go from Interviewer with a capital I, a stranger with an awkward amount of power in your short-lived relationship, to an anonymous confidant. They don't know you, but you seem pretty cool so 'fuck it, let's talk.' That's legitimately the attitude I want my interviewees to have.
6. Relate early and often. This one's tied to #4 and 5, and it's kind of hard to describe. But you'll know it when it comes up. If you seem relatable and likable, and like someone that your interviewee might want to open up to, they'll tell you something pretty early on that makes them feel a little vulnerable. You'll sense it. You'll feel them feeling like they're oversharing, like they're telling you what's important to them and and not necessarily what they think you want to find out.
It's a critical point; it's crucial to building and maintaining that liminal space. If you seem judgy or even slightly critical, you're back to being the Interviewer. Hold the space and demonstrate that you understand them and the moment. I like to basically repeat back what they've said in that moment: "Oh, yeah. Word. It's not that you want to leave them at the sitters all day, but that's just how it has to be sometimes, right?" And the interview opens up.
7. Don't be afraid to throw out the interview guide on the fly. Depending on how pressing and particular the info that you need to collect in your interviews is, you may have to stick to the script. But if you stick to my script (be more human, overshare, relate early and often) there's a good chance that your interviewee will open up (almost like a mini-therapy session) to the real good shit: what's important to them, the interviewee, on the topic vs. what you thought was important to you. You may find that those two things are different, but once you can sense that, you should chase what's important to them. That's the stuff you can message to in advertising, and use to really understand people, their lives, and their relationships to your brand and your category. That's your rocket fuel.
I once asked three questions in a 90 minute interview before it went off the rails and I tossed the interview guide to the side, because my interviewee found her outlet in me and was ready to dish. Keeping your larger goals and purpose in mind, you can let it ride, learn about what's really important to this person, and even use that to iteratively tweak your interview guide for ongoing use. In this case, I took the experience with that woman when the interview was over, quickly added in some new questions, rewrote a few others in the interview guide, and tested it out in the next interview. Guess what? This person was ready to talk about the same kinds of problems (slightly different, but in the same realm), and I'd found a kernel of emotional truth beyond what I thought I was looking for.
8. Pregnant Pauses. They're questions in themselves. People will keep talking to fill the void.
9. Guide rather than drive. Learned that from my driving school instructor 12 years ago. An overly twitchy, controlling death grip on the steering wheel at 75 mph ain't going to work. Loosen up, relinquish some control, and let your interviewee help steer the conversation.
10. Practice. Talk to strangers. Ask a question or two that you've been wondering about for a client, and then practice letting them take the reigns. Practice relating to them, being likable (as weird as that sounds), and guide the conversation, all without making this stranger think, "This weirdo is interviewing me; get me out of here."
Interviewing is a developed skill, and it takes discomfort, screw ups, awkwardness, and experiencing some shit to hone your craft. I have had some WEIRD, even horrific conversations with people about their lives. But that's another story for another day. For now, just know that getting yourself into weird conversations is great practice to become a great interviewer, and to get to the meat of what's truly important to people. There's the magic.