Harper Lee gave away almost nothing about herself for fifty years. The handful of things she did say about writing have stuck around because they're plain and a little unforgiving. This is the advice, pulled mostly from a single rare interview she gave in 1964.

The Direct Answer
Learn self-discipline first, and be honest about whether you write because you want to or because you have to.
Her clearest thoughts on craft come from a rare 1964 interview with Roy Newquist.

Discipline Before You Call Yourself a Writer

Lee's central belief about writing was almost aggressively practical. She thought writing was a process of self-discipline you had to learn before you'd earned the right to call yourself a writer at all. And she drew a line she didn't bother softening: there are people who write, and there are people who feel they simply must write, and she considered the two quite different animals. She put herself firmly in the second camp. Everything else about her working life grew out of that one idea. The six-to-twelve-hour days, the single-page output, the years of revision with Tay Hohoff, none of it came from a clever system or a productivity hack. It came from someone who treated the work as non-negotiable and then showed up to do it, day after unglamorous day. If you're waiting to feel inspired before you start, her answer is fairly cold comfort: the discipline is the thing you build first, and the writing follows from it.

Know What You're Aiming At

The second useful thing she said was about scale and aim. Lee never set out to write the Great American Novel, and she'd have found the phrase a little embarrassing. Her stated ambition was smaller and much sharper than that. She wanted to record the small-town South she'd grown up in, the people and the slow social rhythm of a place like Monroeville, Alabama, with the same close, patient attention Jane Austen gave a handful of English families in a handful of drawing rooms. Ambition, in her version, had nothing to do with size or reach. It was about picking a world you understood down to the ground and then getting it exactly, unmistakably right. That's a more useful target than 'write something important,' and it's a big part of why the book still holds up. Most beginning writers reach for the whole world and end up saying nothing about any of it. Lee did the opposite. She narrowed her sights to one small county, one summer, one family's crisis, and by going that deep she ended up saying something that traveled everywhere.

In other words, all I want to be is the Jane Austen of south Alabama.

Harper Lee, 1964 interview with Roy Newquist

It's worth noting what she didn't do. After Mockingbird, Lee stopped explaining herself almost entirely. She gave few interviews, published essentially nothing new until 2015, and let the work stand without commentary. For a writer, there's a quiet lesson in that silence: you don't owe the audience a running account of yourself, and the pages are the argument.

There's one more piece of her attitude worth borrowing, and it has to do with expectations. Lee didn't write Mockingbird believing it would sell millions of copies or win a Pulitzer Prize. By her own account she expected the reviewers to be unkind and the book to vanish quietly, and she'd made her peace with that well before it was ever published. That turns out to be a strangely freeing way to work. If you aren't writing for the applause, you can't be knocked off course by the fear of not getting it. She put her head down, did the slow work she believed in, and let the result be whatever it was going to be. The staggering success that followed was, in a real sense, none of her business while she was actually at the desk.

For how these ideas played out at the desk, see the full Harper Lee writing routine.

What You Can Steal