1. I will know exactly what every command or script I run on a system I control is supposed to do - no exceptions. If I don't and are just following instructions, I really need to learn what it means and why. If you need to setup a test system and snapshot before and after to see how things work.
2. I will document a lot. Imagine some poor person showing up after you have won the lottery (think happy thoughts, but watch out for buses just the same). Don't just blindly put down step, put the why down. If I cannot write why I am doing something then I need to think about it more.
The rest just flow from those. Learn to program, be a tool builder, find the best way to learn and dive in, solve problems, and insist on consistent, repeatable, backedup, secure systems.
Do remember though: all your successes will be hidden in the darkness and all your failures will be shown in the full light of day. Its not a fun gig at times.
If you don't have a good boss who can see that you are good at what you do, you will have to be able to speak up if you want to be paid what you are worth.
You want to be a step up from a computer janitor who needs to be told what to do, to being someone who delivers value to the business and helps people get their jobs done, and can anticipate problems before they occur.
And on the software engineer/developer side of things the same applies. This is why whenever I am given a self-assessment or asked to help with a review of myself, I go back through my git log, email, etc. looking for what I've done instead of just attempting to summarize based on memory. Then I keep a personal copy of my self-assessment. That way, I have a record of what I did, and so does my company. Wikis, file servers, and other document repositories change, and when you switch jobs, you have that available to look at to update your resume. If your company doesn't make you do at least annual and hopefully quarterly self-assessments, you should do it on your own.
1) I have more years as a developer than system admin (11 vs 7 and 5 as something I'm still not sure).
I've been in my present position five years. Knowing where the bodies are buried (because I buried half of them) turns out to be one of my most useful functions, and whenever I am asked such a question I add the answer to the internal wiki ...