You'll learn the technical concepts and rubrics eventually on your own; here is what I'd be thinking about to start:
1) It's great that you ask and seek to learn to do it right; that's a first step many don't get past.
2) There are big differences between hacking on something at home and professional system administration. Most important is cost: Your time is expensive but system downtime can be incredibly costly. [1] You need to anticipate and prevent the problem in the first place (you are the expert!), have resources prepared in case of failure (including expert knowledge of the system), and resolve it quickly. Also, you are paid as an expert to get results that boost the bottom line. You can't spend a day fiddling around with something and gratifying your curiosity.
3) There is a very wide range of knowledge and skill among sysadmins. You don't need a license to do it; anyone can print "System Administrator" on their business card. There are many, many ignorant hacks; lots of decent ones who don't think beyond what they are told; and few true experts. Who you surround yourself with will determine, to a great extent, where you fall in that range. You probably will adopt their standards and you will learn their way of doing things; you can spend your time learning either the knowledge and techniques of the hacks or those of the experts.
4) Invest the time and effort to learn core technologies [2] exhaustively and to learn best practices. Never shy away from difficult technical material; push yourself to find the best sources and develop skill to understand complex material. Most of what's on the Internet is bullsh-t from and for amatuer hackers, good enough for your home server. You can spend your career without understanding much of what you are doing -- there's enough work out there for the hacks too. Find the very best sources and people (see #3), and take the time to learn from them. Learn something once and it pays off forever.
5) Learn to solve problems. Worry less about learning techniques (e.g., arcane details of command line switches); anyone can look those up. The real challenge is staring at a screen, seeing something that you have no idea about (and which is not in books or on the Internet), and finding a way to solve it (with all the time and other pressures mentioned above). To do that, you need a model in your mind, a deep understanding, of the technologies and systems involved (see #4).
6) Put yourself in situations where you will be in command of the situation and with time in reserve for making major enhancements, learning more, and for unexpected crises; not where you are struggling to keep up with a flood problems, frantically treading water (or slowly drowning). Also choose situations where you are prepared to handle the worst-case scenarios: When the sh-t hits the fan -- when all your plans and normal operations go to hell -- people will look to you to save them. Be their hero. (See #5.)
It can be a very intellectually stimulating and gratifying job. In every field, good people and true experts are hard to find. Make yourself into one and you will be in good shape.
---------
[1] Consider the cost of 1,000 people not working (avg hourly rate * 1,000 * hours), hours of orders missed, facilities shut down because your system is the bottleneck, deadlines missed, angry customers, embarassment to the business and its executives, etc.
[2] What the core technologies are for you will vary. You can't know everything. Beware of investing time learning about technologies that change quickly. TCP/IP probably will stick around for awhile; the app-of-the-week, maybe not.