I believe that the most important thing that served me back then was:
Not being afraid to ask: there's always more thing that we don't know than things that we know. And it's especially true when you start (but it always remains true). So go ahead, think about the solutions you might develop, and ask for a review even before starting coding it, have a discussion with a more experienced dev to challenge your thoughts, and his/her answers will help you a lot learning new things and understanding what you might have missed or overlooked (it's normal, expected and OK)
In other words: a mistake you should avoid is being afraid not to ask for help, trying to be perfect.
Keep in mind that there's every day more new things that come out and you don't already know, than things you learnt during the day. Consequences: never stop learning, never stop at least reading updates to have an idea of what's going on and what you might consider digging for future projects. IMHO being aware of his own ignorance, and trying to have an idea of what's going on is the most important things to have a chance to stay up-to-date.
That's high-level ideas, but I think it was true 15 years ago, it's still true today and chances are it will remain true in 10 years from now. (But, since I do ignore a ton of things myself, I also might be totally wrong ;-)