Having read the Iron Kingdom, The Rise and Downfall of Prussia by Christopher Clark I've taken quite an interest in Prussian culture and civil life (my surname is Winterfeldt and my family immigrated to the States from Prussia- this is a personal interest).
I have however had the worst time finding any sources, original or otherwise, regarding these virtues. With Prussia so associated with notions of discipline, thrift, and toughness (among many others) I'm frustrated with the apparent lack of anything that really addresses these values such as a Prussian ethics book or perhaps a work on how men are to conduct themselves (or something akin to an officer's manual?).
I'd really appreciate some direction and help in this regard- please and thanks!
One of the places you might look into for primary sources are the various tracts and theological writings associated with Pietism. Although Pietism did not originate within Prussia, Spener's University of Halle became one of the centers for this branch of sober Lutheranism and became very influential among the elite of Prussian society during the eighteenth and early nineteenth centuries.
A lot of writings on the Prussian character are dominated by the judgmental maxim "Prussia is an army with a state" and thus look for signs of retarded or authoritarian political development. Two monographs question the premises behind these assumptions. Firstly, although a bit dense and jargon-filled, Matthew Levinger's Enlightened Nationalism: The Transformation of Prussian Political Culture, 1806-1848, covers nineteenth-century Prussian intellectual ideas and shows how they rather than being hidebound reactionaries, Prussia's leading intellectuals were attempting to synthesize Enlightenment precepts to fit into a new national context. Rebellious Prussians: Urban Political Culture under Frederick the Great and his Successors* by Florian Schui demonstrates that the Prussian burghers had a much greater independence and the autocratic state did not always run roughshod over them.