Thank you for a great answer.
Seems most others answer the wrong question, either "how can a junior developer get to where I am?" (which was where my thinking went at first and why I felt uncomfortable giving an answer) or "what would I like my co-workers to be like?"
I would only like to add regarding point 1 that you also have a right to expect an environment where you are comfortable to speak and if that isn't the case it's never your fault. Any place where they think this happens automatically just because "we're all good people" is probably wrong in this, it needs to be actively encouraged.
So I guess the best advice I can give to juniors is that if there is something you want to change then "change your workplace or change your workplace." (don't remember who I'm quoting/paraphrasing)
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