After having read various materials on sharpening, including Bruce Fraser's seminal work on the subject, I have accepted the fact that I am simply never going to understand it well enough to be facile with sharpening tools. For that reason, I use PhotoKit Sharpener from Pixel Genius for most sharpening needs when using PS.
The problem is that that wonderful plugin does not work for NX. So, if I want to print from NX, I am on my own.
Jason Odell, in his eBook on NX, recommends the following sharpening routine for output sharpening:
Create USM step with settings of 64/2/4 and set the Opacity to 70% in the Luminance Channel; and
Create a High-Pass step with Radius of 2 pixels, change the Blending Mode to Overlay, and set the Opacity to 50%.
He recommends these settings when printing with an inkjet printer on glossy paper for an image at 300dpi.
These settings work pretty well for most images printed on glossy or satin/pearl papers. But, I print a lot on matte paper, and I am not sure how to tweak these settings for matte paper, or how to tweak them for images at 240 and 180 dpi.