I'd start with some paper guide - maybe Peter Norton's Guide to Linux (google for it). In fact, I didn't read it, but never put my hands on better written guides than Norton's.
Then google for "wiki util linux", there you'll find a longer list of commands.
Then open your terminal window, read man pages of the commands ( man somecommand ) you learned, liked and decided to use in the nearest future, and, of course, try them. In my opinion, the most important part is "decided to use in the nearest future" - you know, human brain is a smart creature, keeps only useful things ;o)
Have a look at the following pages:
<a href="http://www.brighthub.com/computing/linux/articles/7116.aspx">The Beginner's Guide to the Ubuntu Terminal - Part 1</a>
<a href="http://linuxcommand.org/learning_the_shell.php">Learning the shell</a>