Questions concerning smooth modulations, especially how to effect them, keep coming up in my own efforts at composition. Apart from Max Reger's little treatise (which in some ways is and in other ways isn't helpful), are there any other books specifically on this subject? Or at least a harmony text that delves into this subject extensively. To be clear, I don't need more information about pivot chords, etc., but rather on how to prepare the ground for my modulations in a smooth and convincing way, and on how best to confirm the new key.
Frank Shepard has a book on the subject: How To Modulate." It's available on the internet: https://archive.org/details/howtomodulatesim00shep/page/n4