How to export pictures in Lightroom is not the problem, but what %-quality option to choose is important for the size of the resulting files. Specially when exporting to show them on a web page, the size is still the most important thing to take good care of. I noticed that pictures with a size much larger than 150Kb lower the user experience when browsing through them.
I tried to optimize my export options according to this but could not get a good result. Changing the option sometimes did not result a different size of picture at all. Search about this topic reveilled that Lightroom seem to give the option of 0-100%, 101 steps, but couldn’t care less about changing the quality from 99% to 95%. I happens that Lightroom “translates” the 101 steps into 13 steps. This web page has a very good look at the problem with many examples, which also show that size aware exporters should also consider very much the contents of the picture.