Nightshade Prequels by Andrea Cremer
Rift and Rise
Since these books were published as prequels I read these first. I will say that you don't necessarily have to. These give you further insight into how things began but the trilogy can be read and understood without reading these first.
I absolutely loved every minute of Ember's story. These books are very well written and the characters feel so real. The only negative thing I can say about these is that there isn't a third book! I would really love to have more of Ember and Barrow's story.
Overall, I was not disappointed with these books at all.