In 2009 Massimo Vignelli generously released a free pdf document: The Vignelli Canon. If you dig around, you'll probably find it online somewhere. The Canon was a summary of what he considered to be essential knowledge that all designers should know, underpinning the idea that, "Creativity needs the support of knowledge to be able to perform at its best".
Vignelli is the quintessential designer's designer, championing a signature modernist approach that can feel a little soulless when practised without a deep understanding of the task at hand. But, of course, Vignelli is the master. Whether you're a dedicated modernist or not, The Canon is essential reading. A year after his electronic version, the print edition became available.