Root-me.org: There are challenges in several categories, and they’re quite good. There is no clear pathway through, though, so it’s up to your hackerly curiosity to explore your interests. https://www.root-me.org/?lang=en
Shellterlabs: Work through a series of lessons to gain competencies in one area after another. The challenges are truly challenging. https://shellterlabs.com/en/
TCP/IP models, important ports, proxies and firewalls
Begin a Maltego investigation (graph) of yourself. Start with the Person object and expand outward to work information, email addresses etc. Every single particle of information you can gather about yourself, anyone else can too.While this kind of scanning is perfectly legal in many parts of the world (think about what ad agencies know about you), remember this critical hacker principal: Don’t attract unneeded attention.
Take your first reading pass through Chapters 1, 2 and 3. Highlight liberally. Plan for using special markers in locations that directly discuss test topics (i.e. questions).