Is the image for print or web display?
if it is for print and is already resized for the print format, zoom in to 100% and increase the values till it looks slightly oversharpened...it will look fine for print...
for web, at 100%, adjust till it is just right...
last point...its good to do sharpening at the last stage of workflow, after you have decided on output format and have resized it to that format...cause resizing does affect sharpness of image...and might exaggerate sharpening halos...