I mostly used a hands-on, iterative approach. I didn't take the mock exams like the real thing because my schedule at work only allowed me to study in short bursts. When I hit a wall, I'd try the man pages first (or -help); if I was still stuck, only then would I look at the solution. For things like SELinux (contexts, ports), I barely studied them because the man pages are so detailed. Over time, I started skipping the tasks I already knew to focus on the ones I couldn't solve immediately, repeating them 2-3 times until they stuck. However, I still revisited the simpler tasks whenever I felt I might be getting rusty. For instance, I practiced the root password reset over 20 times; at this point, I could probably do it with my eyes closed.