A large part of it is learn as you go, but if you can learn the programs you will be using such as vim or nano/pico and bash and how linux works (for you specifically how ubuntu/debian do things) it can help a lot.

As for specifics there is a lot of good stuff in here: http://www.debian.org/doc/manuals/debian-reference/

If you come from windows avoid using X and GUIs as that really shouldn't be needed in a server environment.