I learnt not to try and do/invent everything myself (initially, at least - 'til I felt I sort-of knew what I was doing).

I learnt that there are rules and means, with good reason.

I copied - not absolutely, not directly.

I learnt to value the feedback of people who I trusted.

I learnt to ignore the urge to please everyone, all the time.

Oh, and the client's not always right. They're always right to have their view, but they're not necessarily right about what that means. That's what they're paying me for.