LinuxQuestions.org - Carrier in Linux

Well to start, you may want to learn how to spell "career".

Anyway, wipe your system of Windows/OSX and run Linux solely on your computer. Learn how to do everything in it, and I do mean everything. Do not drop back to Windows/OSX unless you need to run a specific program that is only available in Windows and has no Linux alternatives, then immediately go back to Linux when you're done. Practice networking, SSH tunneling, user administration, installing programs through the package manager, compiling/installing programs from scratch (even if you don't have to for your distro), etc. If your machine is powerful enough you may want to set up several Linux VMs and network everything together, set up Nagios, etc.) You may consider studying and getting certifications as well. Practice with distros using multiple package management systems (RHEL/CentOS, Debian, etc.). You WILL break things, learn from your mistakes, what did you do to break the OS, why did you do that, how can you avoid it in the future, etc.

I do not technically have a "Linux Administration" job, I'm an EE who does embedded systems development, programming, and also happens to build and maintain the Linux network at my job, but if I were looking for somebody to take over the Linux systems admin side of things, the above is what I would be looking for.