In no particular order:
Typography and Lettering
Just My Type Simon Garfield
Twentieth Century Type Lewis Blackwell
An Essay on Typography Eric Gill
Stop Stealing Sheep & Find Out How Type Works Erik Spiekermann
A Treasury of Alphabets and Lettering Jan Tschichold
Twentieth Century Type Designers Lund Humphries
Why Fonts Matter Sarah Hyndman
Other related
This is an must-read (old, but still relevant, possibly even more so today):
Design for the Real World Victor Papenek
Do Good Design David B Berman
The Green Marketing Manifesto John Grant
500 years of printing S. H. Steinberg
On Brand Wally Olins
Frank Pick’s London V&A publications
Bit more left field, but important
Read books on the history of the Bauhaus (there are many)
These following three are primarily architects and furniture designers, but you can learn a lot about design and proportion.
Le Corbusier
Frank Lloyd Wright
Rennie Mackintosh
Also, read as much as you can about print production.
I am sure others can add to this list as there are bound to be some glarers I have missed. It is in no way a comprehensive list. I just looked at my bookshelf and listed some of the books I have read in the past.
Hope this helps