Always understand what you are doing, never accept advice like 'do it exactly like this to be on the right side', in short: stay clear of vodoo. Learn scripting to avoid repeating yourself, learn templates/macros or whatever it takes to avoid code duplication (it takes an effort, but is really worth it). Have some kind of document where you can write down your experience, what was learned, what kind of problems you have solved - patterns keep repeating and writing stuff down helps to be aware of these patterns. Try to learn reading code - it's a skill of great value. Learn specifics of build tools as a lot of time gets wasted if the tools are not understood
Be a bit sceptical of people who pass out judgement and advise
On second thought I don’t like my answer any longer: your knowledge and skills are conditioned on the environment where you were functioning/working. A slight change of environment and most of your assumptions and knowledge is out of the window.
What is important is a willingness and skill to learn new stuff; all else is in a flux.
Also I don't like this distinction between junior and old hands; it can make you complacent.
Be a bit sceptical of people who pass out judgement and advise