I'd suggest building a "large" home network.
I have something like (on and off) 8 machines running set up to be routers and nodes and stuff.
You get a lot of practice that way.
PLUS: You can take known vulnerable programs and see how they behave when put under stress.
If you break your own stuff no-one will want to get back to you.
Doing that on a job is a bit tricky, cuz you can't try that much in a production environment...
