The Exposure Time Tables pocket reference book by Zeiss Ikon was the go-to guide for working out how to snap your shot. As Peta Pixel explains:
There are 5 steps (i.e. things you need to consider) on the path toward determining your proper exposure time: time of day/year, lighting, object to be exposed, dryplate/film, and aperture. Each step provides you with a number. After the 5 steps, add up all your numbers and then look it up on the chart to figure out your exposure time!
The process was apparently developed by a photographer named Dr Max Leo, and it has long since been abandoned. Still, if you fancy finding out a little more, you can read a PDF of the whole manual here. [Camera Manuals via Peta Pixel]