There's no substitute for apprenticeship (by whatever name). Unfortunately, skills of this kind may be close to extinction. For someone like you just interested in getting better at layout design, I'd recommend something like 'The Elements of Typographic Style', by Bringhurst; this concentrates mostly on books, but much applies to other layouts. Of more general interest -- i.e., beyond layout design -- might be 'An Encyclopedia of the Book', by Glaister. There's a wealth of valuable design and print resources from the '60s - '90s if you can find them -- some libraries still have high-quality examples, but most have replaced them with much less-valuable contemporary resources. Look for book and magazine sales by university departments, businesses, etc.

Thank you! I have been absorbing Bringhurst methodically the past year.

I had not heard of Glaister, will be on the lookout.

Good point about library and corporate sales. My main supply of materials from the 60s has been from estate sales -- not for instructional materials, but for well composed period pieces. Older letterfaces and color palettes are so evocative; seeing the label of a 70 year old oil can with so much more personality than the products of today makes me want to bottle this style for my own future use. And it feels good to hold something back from the landfill.