I'd recommend "The Art and Science of Smalltalk" by Simon Lewis.
Because it's so old, Smalltalk does things very differently to other development environments.
The GUI is strange by today's standards (Smalltalk was why Xerox developed the GUI - you can see how much extra work Apple did to make the windows/icons/menus that we use today).
And it uses an image (which is sort of like developing in a VM, and then copying that VM to another machine to deploy).
So diving straight into a Smalltalk may leave you a bit lost - whereas the book is quite a good primer on OOP in general and where those OO patterns came from (whether Squeak, Pharo, GNU or one of the big expensive implementations).
