I have no idea if this will work for everyone, but this is how I became a UNIX (and later Linux) geek:
- Read "The UNIX Programming Environment", Ch 1-5 at least. An excellent introduction to the philosophy of UNIX as well as the basics of using it as a user and later a programmer.
- Get a copy of "UNIX Power Tools" as a desktop reference; however you aim to read it all.
- Make sure you have a network connected UNIX/Linux system on which you can lavish loving care and practice your new skills
- Keep reading books, manuals, articles, blogs, forums etc etc.