The Divergent Trilogy by Veronica Roth is a great book trilogy (apart from her killing off all of the good characters except Four and Christina). They teach us many things like being different is not a bad thing, the ones you love will not live forever and we all make mistakes in the heat of the moment.
The Infernal Devices and The Mortal Instruments by Cassandra Clare are also wonderful series Cassie is such a great writer and she describes characters really well. I love how she doesn't make it seem like you have to be an absolute tomboy to save the world and you can wear 7 inch heels, long dresses, be beautiful and have a boyfriend but still be a badass and save the day e.g. Isabelle Lightwood.