Hi and welcome to LQ.
1. Printed books tend to go out of date quite quickly and while there's lots of principles/linux commands that have not changed much over the last years, it might be better to use some up-to-date online resources (which are free of charge by the way)
2. Again, while there are a lot of linux commands/configuration files that are not distro specific, there are areas where a recommended way of doing a task will be different across distros.
I think you need to be slightly clearer about what exactly you are trying to master. It'd be good to pick a distro (some good server distros are CentOS, Debian, Slackware)
If you google 'linux administration tutorial' you'll get tons of links to free resources:
Have a look at this (As an example):
On a side note, personally, I find that it's easier to learn if you set yourself particular tasks to complete and learn as you go along.
One of the best ways of learning is to visit this forum frequently (for you perhaps the newbie section) and read the questions that people post and the answers they receive.