If you could start your career over again, what would you do differently?

What they are really asking

When they ask what you would do differently if you could begin again, the interviewer wants to know whether you reflect on your own path, and whether you're basically happy with where you've ended up. Someone who would change everything sounds lost. Someone who would change nothing sounds like they've never thought about it. The sweet spot is a person who likes their direction and can name one or two things they'd do differently along the way.

Keep the change about you, not about other people. "I'd avoid my second company because the boss was awful" turns the answer into a complaint. "I'd have moved into a bigger team sooner" is about your own choices, and it's something you can learn from out loud.

A shape that works

Keep, change, what you do now. Start by saying you'd stay in the same broad field, if that's true. Name one thing you'd change: a habit, a timing, a skill you'd start earlier. Explain what it cost you. Then say what you've done about it since, so the answer ends with action instead of regret.