If you're even remotely into reading books on self-improvement or "modern" philosophy, The Almanack of Naval Ravikant is the one book you absolutely must consider reading.
It's available online for free. Physical copies cost a little bit of money (obviously). But given the value that I feel is inside the book, the price is extremely reasonable.
I first learned about Naval from his interview on the Tim Ferris podcast. It's always a treat to listen to someone who looks at things from a first-principles point of view. Plus he has this rare ability to express a ton of insight using an easy to understand language. In the sense that when you've listened to what he's saying or have read one of his blog posts or tweets, sometimes you go "that makes too much sense".
So when I came to know that this book is available on Amazon, I ordered it right away. And already a few pages into the book, I had the feeling that this is going to be one of my all-time favorite books. Mostly centered as a guide to wealth and happiness, the contents of this book cover a lot of ground. At no point though does that impact the core ideas that this book is trying to convey. There really are a ton of things to learn from in this book.
Content-wise, the book comprises of some of Naval's best tweets (and the "tweetstorms"), essays and interviews. The flow from one topic to the next is very fluid and you should easily be able to finish it in a day or two. But even though it's an easy read, you'll most certainly find that this book requires multiple readings to be able to fully grasp and internalise the ideas expressed. Like how it is with most classics.
TL;DR: read it!