I have acquired a useful book on genealogical research for my personal library: The German Research Companion, by Shirley J. Reimer, Roger P. Minert, and Jennifer A. Anderson. This third edition, published by Lorelei Press, contains 706 pages, and includes basic and advanced material about doing research on German ancestors both in the United States and in their original German-speaking regions.
Section headings in this book indicate its scope: German Lands, Past and Present; Tools, Contacts, and Resources; Emigration and Immigration; United States Resources; Language and Vocabularies; German Resources; Archives; Life in Our Ancestors’ Times; and Newspapers, Libraries, Museums, and Other Information.
In the section, Life in Our Ancestors’ Times, there is an extensive discussion of names and naming patterns, given names of Germanic and foreign origin, and name days. Reading this discussion cleared up for me why one of my German ancestors, Johann Matthias Flaugh, was generally known as Matthias rather than Johann.
This book is available from http://Amazon.com and other online booksellers.