Bringhurst has already been mentioned, but before that what helped me was to learn the vocabulary. Knowing what Spur and Spine are, being able to distinguish be

Bringhurst has already been mentioned, but before that what helped me was to learn the vocabulary. Knowing what Spur and Spine are, being able to distinguish between Counter and Eye, having an idea about Humanist and Rational, etc. The point is not so much the terms but learning their meaning makes you see a world you didn't see before. It will even be impossible to "unsee" it once you have it. It will help you to understand a lot of typography talk and help to distinguish between serious arguments and the nonsense talk, which undoubtedly is prevalent in design discussion. My school in this regard was the early fontblog.de, but this was 15 years ago and I couldn't find a good example in their archive. It was all in German anyways, so not so helpful for most here. A more recent resource is maybe Stephen Coles' "The Anatomy of Type" which gives a compact overview of the important terms, has tons of examples and a good introduction to a basic set of standard typefaces.