Rationale Design is a studio based in San Francisco. They have unleashed these magnificent graphic design books. Prized books full of knowledge that can be used by graphic designers for research and educational purposes. All of the files can be found on the following link. These books will come in handy if you are trying to step your game up.
Graphic Design for Non-Profit Organizations

The document presented here focuses on improving structural design and general best practices for Non-Profit Organizations. However, the scope of the teachings apply to achieving good design across any industry.
Designed by Massimo Vignelli & Peter Laundy in partnership with AIGA, 1980, 52 pages.
Dot Zero – Issue 1

The document presented here is Issue 1 of Dot Zero magazine. Dot Zero acted as the house publication of Unimark in partnership with Finch Paper. Unimark was cofounded in 1965 by Massimo Vignelli, Ralph Eckerstrom, Wally Gutches, Larry Klein, Bob Noorda, Jim Fogelman, and Bob Moldavsky.
Designed by Massimo Vignelli, 1966, 29 pages.
Deutsche Bank design manual

Presented here is the “Erscheinungsbild Deutsche Bank Typografie” design manual, articulating the design systems for Deutsche Bank. Includes typography, grid, color, logo, stationery, and general design guidance.
Designed by Anton Stankowski, 1978, 69 pages.
New York Botanical Garden design manual

Presented here is a comprehensive yet compact design manual outlining the graphics standards for the New York Botanical Garden. This manual illustrates a program for standardization of signage and many other communications for the gardens.
Designed by Massimo Vignelli, 1973, 32 pages.
Last but not least, my personal favorite.
Sean Wolcott: Graphic Design

“Sean Wolcott: Graphic Design 2008–2014” chronicles the ongoing design work of Rationale’s founder. Includes projects ranging from identity, promotion, publication, user interface, packaging design, previously unpublished works, and more.
Designed by Sean Wolcott, 2015, 172 pages.