Apart from books don't forget the internet can be very useful. Some books that have helped me are "Complete UNIX guide", "Essential System Administration" Apart from that there are a few others, depends what kinds of things you need to learn/know first.

Example I needed to learn administraion and networking (still do ) and backups. Started with a few books like the above sat down infront of a Solaris box and played around.

Personally the best way for me was to set myself a little task learn how to do it. Then go to a test machine and try it in practice. Of course this only works if you have a machine that you can crash and burn. If there's no crash and burn machines be very careful with what you do to a machine.

Don't forget the 'man' pages are a good place to start with Unix. (In case you don't know about the man command it stands for manuals, to run the command something like this "man ifconfig" that will show the manual/help pages (whatever you want to call them) for the ifconfig command)

Don't forget search engines (www.google.com). They are always a good little tool for finding stuff. A good website is docs.sun.com others will have others but I like that one.

Or you could just hit work up for some starter courses and learn the easy way