List ways in which scholars look for clues ranking the methods from what you think would be the most useful to the least useful

Scholars ie those who for example look into history and study the features of say ancient civilizations,are partly evaluating different methods of doing things that different peoples used say in the past. An example could be, in my case of studying the ancient mining practices of the 1500's is that the clues to the methods were learned by a famous doctor Georgius Agricola who studied the methods like setting fires underground to break the rock (before explosives) and by studying the machines the early miners used to dewater the mines ie pumps powered by waterwheels for example.

Be more specific so i can

Require the nobles and clergy to pay taxes.