In the Lightroom Export dialog, I recommend
"Sharpen for Screen" in the amount: "Standard".
File Settings:
JPEG, SRGB, limit file size to 'X', where X will usually, but not always, be somewhere between 500kB and 2000kB. I aim for under 1000kB if possible, but it depends on the detail in the file. Files with less detail can tolerate more compression.
Fun Experiment: Pick a visually 'busy' shot that has lots of detail, fix the pixel dimensions at 1200 or 1600 across the long side, and export(create) 3 JPEGs at 50kB, 300kB, and 1000kB. Examine each one to see the effects of the JPEG compression.
**I try to make the file size as small as possible(to economize space on the Nikongear.net server) and still maintain adequate picture quality.