I don't think anyone knows what every single script and command does on a system.
Has anyone read and audited all the init scripts for example? Never.
And where would one find the time to do this? Certainly not on the job.
Most valuable advice I can offer is: learn an editor and use it for everything.
OpenSSH is boss for all networking issues.
Netfilter (iptables) once understood is used daily.
And something I call "The 2s Complement": know two of everything, two distros (RPM and .deb), two shells (bash
and zsh), two MTAs, two... you get the picture.
In every environment you will be able to perform then.
Use zsh with GRML completion, saves so much time.
For hacking, read all Phrack issues.
Know shell scripting and at least one other interpreted language like Python, Perl, PHP, Ruby.
Don't waste time on desktops, changing looks etc. I wasted so much time early on customising everything, great fun but no ROI whatsoever.
But the most important thing is... how to think!
That that my friend takes a long time and only you can construct your own effective thought processes and algorithms.
Build terse mnemonics to aid in command options.
Oh yes, keep everything you code, script etc. for future reference and learning and improving.
Learn to code and then learn to think in code when sysadmining systems. Infrastructure as code.
Another thing, build scripts, configurations, solutions etc. as objects and reuse those objects, eg. a rsyslog configuration stanza for a UDP input that is portable and can be reused.
Sorry for waffling on I can think of so much more...
Start a blog and copy/paste your ideas and interesting work configs, code, scripts etc. there.