Like ludvig said make your self an environment. I would start off by deploying and getting familiar with lamp as well as learning scripting (bash or perl). I would use either xen or vmware as hypervisor wich will allow you to deploy anything you like. Youll be able to practice disk management raid, encryption, ect. It also a good idea to get the hang of virtualization as it is the future in system administration. You can practice storage aswell install freenas or openfiler on a vm and create a bunch of virtual disk. The sky is your limit just get curious. You should get familiar with security, like locking down ssh, and using iptables. i can go on on but just get curious and u will be fine. It always good to look at job posting and go to interviews even though you know you we wont get the job but u will get the feeling of whats in need in the market.