I am currently reading The Art of Frugal Hedonism. The authors bill it as "a guide to spending less while enjoying everything more."
And indeed it is!
There are lots of cool ideas and nuggets of wisdom in there. But it is, as the title explains, a book about frugality. It is not about investing or earning more money.
It is also a hilarious book full of silly turns of phrase and funny photos!
I highly recommend.