If you can afford it, Certification (RHCSA as above) will help a bit to get noticed by HR at least.
RHEL is pretty much the std in commercial systems(but you need to pay for it), and Centos is a free rebuild, so you can start learning that.
You should probably ask the Mods via the Report button to move this to the Certification forum.
You should start looking at the manuals at www.linuxtopia.org
, especially the Admin section.
You're going to need a fair bit of luck, as you really need experience as well.