Source: Sharpening in Adobe Camera Raw and Lightroom – f64 Academy by Blake Rudis

These 5 steps you may use as a starting point either in Lr or ACR:

1. Drop the Sharpening sliders down to zero… all of them!   Afterall we do not want to be reducing our noise reduction efforts while seeing our sharpening, that would not be helpful for either.
2. Address the Luminance and Luminance Detail.  I tend to keep these pretty close on every photo.  Whatever Luminance Detail I set, I usually set the Luminance to half that.  So if 50 for Detail, then 25 for Luminance.
3. A Healthy dose of Color Noise Reduction and Color Detail is a good idea.  Most of the “noise” in noise comes from the color.   Reducing the color noise all the way can usually produce what looks like grain rather than noise.  Sometimes I just reduce the color noise a great deal and call it a day if I like the grain that is leftover.
4. Now you can address the Sharpening, but start with the Mask FIRST!  The mask slider has this mysterious hidden hot key. Pressing Alt (Option on a Mac) will show you where the mask is affecting the photo.  Hold that hotkey while you drag it over and when all of your detail is in white and your smooth surfaces are black, you should be good to go!
5. Hit the Amount, Radius, and Detail simultaneously.  There is no magic bullet setting here.  I use these three at the same time and dial in my sharpening with them as a set of sliders rather than individuals.  Amountis how powerful the sharpening is going to be.  Radius is how many pixels around the sharpened pixels is going to be, the smaller the number the more subtle the sharpening. Detail is the amount of contrast between the sharpened pixels, or how light and dark those pixels are going to be as a result of moving it.