In the 1950s British Transport Films produced a series of films about driving DMUs, and also about fault finding which is very important knowledge for a driver if something goes wrong.
These films can be found on YouTube:
The Diesel Train Driver - An Introduction To The Diesel Train
The Diesel Train Driver - Driving The Train
The Diesel Train Driver - Dealing With Faults
The Diesel Train Driver - Operational Requirements
Another interesting BTF film (this one in colour!):
The following pages contain notes supplied by Stan Acaster (Dean Forest DMU Group) and were compiled using extracts from: 'Questions and Answers on Multiple Unit Diesels' by S.E. Webb, The British United Traction Ltd., Service Manual for 'A' Type and 'L' Type Units by B.U.T. and the Service Manual for the R14 4-speed gearbox by Self-Changing Gears Ltd.
Preparation and Basic Technique General Information that a Driver SHOULD Know
Some Do's Dont's and Remembers
What do I do if...?
Effects of Jumpers Becoming Disconnected