And I started with a book... haha, try the handbook > admin.com
If you're used to Windows system, I find that it's easier to learn the fundamental concepts through a book. Try also some Linux certification books and handouts for some nice how-to's, problem solving techniques and quick references.
Although I agree with everyone. This is very similar with learning programming techniques. Learn by getting your hands dirty, setup a virtual machine, do stuffs, download packages, configure them, destroy them and fix them.