Most people mean to do this and never do. Not from indifference — from not knowing how to start without it becoming strange.
Because it is strange. You sit down with someone you have known your whole life and announce that you would like to interview them, and immediately you are both performing. They give you the tidy version, the one the family already knows, and you write it down, and neither of you enjoys it.
The problem is the question, not the person
"Tell me about your childhood" produces almost nothing. So does "what was it like growing up". They're too big to answer. Faced with a question that size, most people say something general and true and completely uninformative — "oh, we didn't have much, but we were happy" — and the moment closes.
Ask instead what the kitchen smelled like on a Sunday. Ask who lived next door and what the father did. Ask what they were frightened of at nine.
Small questions get long answers. Big questions get short ones. It's the opposite of what you'd expect and it's the whole technique.
Ask about objects and routes
The most reliable openings are physical. What was in the front room. Which way did you walk to school and who did you meet on the way. What did your father wear to work. What was the first thing you ever bought with your own money.
Memory is stored against places and things far more than against dates. Give someone a route to walk down in their head and the details arrive on their own — the shop on the corner, the dog that barked, the name of the woman who ran it.
Let the silences run
This is the hardest part, and it's where most people ruin it. Someone pauses for four seconds and the interviewer jumps in with another question, or worse, with a suggested answer.
Those four seconds are the person actually retrieving something. Say nothing. Look mildly interested. The thing that comes after a long pause is almost always better than the thing that comes immediately.
Don't correct anything
Dates will be wrong. Two stories will contradict each other. Someone will misremember which sister it was.
Let it go. You are not building a court record, and the moment you correct someone they become careful, and careful people stop being interesting. If it matters, check it later against somebody else.
Write it down afterwards, not during
Scribbling while someone talks changes how they talk. So does a phone on the table with a red dot on it, however much everyone claims to forget it's there.
Have the conversation. Then, the same evening while it's fresh, write down what you can. You'll lose some of it. What survives is what mattered, which is generally the right filter anyway.
If you do want a recording — and for a voice, it's worth it — ask first, put it somewhere out of eyeline, and then genuinely ignore it.
Do it in ordinary circumstances
Not at the big lunch with fourteen people. Not on the birthday. The good material comes on a Tuesday afternoon with a cup of tea, when nothing is happening and nobody is watching.
And do it more than once. An hour is enough. Six separate hours over a year will give you something that a single heroic afternoon never will, because people remember more the second time you ask — the first conversation goes away and works on them quietly for a fortnight.
The thing nobody warns you about
You will discover that you had the wrong idea about someone. That your grandmother was funnier than she let on, or that the story you'd been told about why the family moved isn't quite what happened.
That is the point. Not to confirm what you already knew, but to meet the person who existed before you turned up.