[upstill]

Find your edges: read at the edge of what you're familiar with. When you have holes that need filling, you inhale the new information like a dry sponge slurps up water. Reading something just because you think you "should know" that area, regardless of how far afield it is from your existing knowledge base, makes it more foreign, hence more difficult to absorb. I've gotten enormous benefit from re-reading the manuals of systems I already use but have mastered haphazardly.

It's a challenge to find material at the frontiers of your knowledge, but the effort pays off in efficacy.