I usually get the most out of a book by reading it with a pen. Any time you come across a passage that you really like for whatever reason, or that you find particularly intriguing or confusing, or with which you really disagree, or that resonates with you somehow, underline it and maybe jot a quick note next to it just so that you'll remember it. Don't hesitate or think "nah, that's probably not that important to the author's vision" or anything like that; if it seems important to you, then it is important. Basically, think of your reading as a conversation between you and your thoughts and experiences and the author and their words. Probe at the text, not necessarily in order to uncover an elusive meaning more quickly like a game of hide-and-seek, but just so that you'll become more intimately familiar with some of its ideas, its style and texture, etc.
It's good to approach a book discerningly, but at the same time, don't become too obsessed with finding its full or authoritative meaning - it's simply not possible. The way that you read and perceive a work is informed by your own stage in life; some insights will pop out at you, and others will pass by. If you re-read the same book a few years later, you'll be struck by things of which you didn't take any notice the first time around. Remember that reading is a very personal experience in this regard, and not only is this okay, this is what makes it so joyful and rewarding in the first place.
I don't know if that helps very much, but it's more or less my own approach.