Some years ago, in a discussion about 'learning Linux', DanielLawson gave me this list of things to do in order to become more acquainted with your Linux machine. I present it now for the first time in it's entirety....

• Setup a www server, with virtual hosts mapping it to your dynamic dns name AND your machines local dns name (if applicable)
• configure sendmail properly to allow outgoing mail, configure the relaying rules so that its 'safe' to leave open on the net.
• Setup a pop3 server that you can connect to from your computer, and recieve mail on, and set up fetchmail to automatically grab your ihug mail for you and pass it to this local pop server
• set up a squid caching web proxy, and set it to use ihugs proxy as a peer cache
• recompile your kernel, removing all unneeded modules and options, and maintaining all required functionality
• learn how tcpdump works
• learn how route works
• set up a local DNS server, and configure it for your local network (and ipt network if you are on ipt)
• join the ipt network if you haven't already
• set up samba to share drives to your windows computers
• set up samba to perform NT-style domain logons, and setup netlogon scripts for every user.
• set up a printer connected to your linux box, and share it via samba to your windows pcs
• learn how socks5 works - properly
• learn how rpm works - build a src rpm for your system, and learn how the .spec files work - play round with them, see if you can create your own src rpm
• learn how wget works
• bash scripting. script everything you can. sed, grep, awk, are your friends. There are many many more tools you can use tho...
• use the man pages and info pages LOTS