On the job experience encompassed paste-up with wax, cutting masks out of rubylith and ruling forms by hand with a Rapidograph pen. Before there were scanners we shot line art and half-tones on the large format PMT camera.
Proof reading for hours on end before the days of spell checker was actually fairly exciting since one never knew what one might find, or not.
Aside from the technical side, I gained customer service skills and estimating experience and became proficient in production management involving several employees.
It was common practice for designers to provide us with tissue layouts to follow or painstakingly calculated copy fit instructions. The classical design training of the prominent designers who frequented the trade shops where I worked were instrumental in shaping my own design philosophies.