EB rewards you when you train your FMs in cities with Schools, the right temples, and if you are able to levy high or very high taxes. This will give them better traits and ancillaries. Of course it depends on the faction you play, the traits of FMs (the most important are the Sharp / Vigorous / Charismatic traits, and the Optimistic / Unselfish / Loyal) and some luck as well.

You can acquire several bad traits as well in the process. As always, you need to carefully consider how to train your FMs. Even if they are useless at governing, they may still be very useful at fighting.