1 - Install some Linux. One of the easier ones until you feel more comfortable. I recommend Linux Mint.
2 - Use Google and Wikipedia, read a LOT and know how to Google for your questions (most probable they have been asked before, yes this one too).
3 - Learn the 30 or so, basic Linux/tech sites and frequent them, besides LQ you have the ones from StackExchange, LinuxForums, Linux Weekly News, Kernel.org, Kernelnewbies.org, the Linux Documentation Project (sometimes a bit outdated but still a valuable tool for learning), and on and on...30 is BASIC sites. Really, read A LOT.
4 - Play with your Linux box.
5 - After reading and playing, you'll have always more questions. Please, DO search on Google and in the forum you are about to ask, if someone already asked your question.
6 - IRC is a good resource too for quick questions, and many times you'll get your answer quickly and interacting in real time with your supporters.
7 - Have patience, learning anything beyond the surface takes years. The more expertise you want, more years.
8 - Have fun :-)
On the practical side, first learn the filesystem, how it is organized, and the shell. The basic commands for filesystem traversal and manipulation, and how to get help on the command line: the "man" command (man man), and "help" for help on the Bash "builtins" (bash is the most common textual shell). "info" is another documentation system in many linuxes (man info). Finally, many packages come with extra doc in /usr/share/packagename or /usr/share/doc/packagename.