I think it's very important to have a feedback loop, where you're constantly thinking about what you've done and how you could be doing it better. I think that's the single best piece of advice: constantly think about how you could be doing things better and questioning yourself.
A Truthful Evaluation Of Yourself Gives Feedback For Growth and Success
Online review sites are the slushpiles of feedback.
Really pay attention to negative feedback and solicit it, particularly from friends. ... Hardly anyone does that, and it's incredibly helpful.