There are a couple of general tactics I use to design non-leading research.
- Feedback feedback feedback! This is the single most important thing, because it's really easy to forget how much more you know about the problem you're trying to solve than the user does. I encourage my team members to call me out when I'm being leading and give them positive reinforcement when they do. When I first started out, I also recorded all of my research sessions and would watch them later to try to catch myself.
- Script critical questions / instructions and have an outline for the session. When you are struggling to construct an instruction on the spot you might be distracted and accidentally give more cues than you intend.
- Non-leading, open-ended questions. Questions should never be yes/no or imply a dichotomy. The most leading question you could ask is "There was a sidebar on the page you just saw. Did you notice it?" Less leading would be "What do you recall about the page you just saw?" Even less leading would be "What did you do to try to accomplish [task]?"
- Silence is your best friend. Every time you open your mouth, you give more cues to the user. When you get in the habit of asking open-ended, non-leading questions, you'll find that you need to talk very little, except to move on to the next topic or prompt somebody to dive a little deeper with a question like "what's good about that?" or the ever-useful "why?"
- Carefully consider the sequence of revealed information. Often you'll need to reveal some of your objectives to dive a little deeper, and you need to make sure you do it in the right order.
I recently designed a telephone interview to see if customers who had signed up for a specific offer were influenced by a particular component of that offer. The team had the question - did customers notice that component? Their thinking was that if customers hadn't noticed it, the solution would be to make it more prominent. Experienced researchers should be hearing alarm bells at this point.
The interview I designed started out very general - understanding their motivations for looking for the product, how they used it, what they liked about it. I gave the interviewer strict instructions not to mention the specific component until the very end of the interview - if the customer noticed that component and it influenced their decision/use, then it would have come up organically in the open-ended discussion of their motivations and use. At the very end, if it never came up, we'd ask if they knew that specific component was part of the offer.
As it happened, it almost never came up organically in the discussions, so we almost always had to ask directly. We found that some were and weren't aware, but it was far more powerful for the team to have started with that open-ended context to understand why customers never noticed the offer component - it clearly wasn't important to their decision to buy! If we'd just asked if they knew about the offering component and if it had an influence on their decision, that would have raised all sorts of churn in the team about how to make the offer more noticeable.