Use unique characterizations. Instead of relying on the common traits of the characters from the original, add some twists. For example, make Juliette more assertive in a different way. Also, create a vivid and detailed setting. If you're using the same world as in the book, describe it with more nuances like the smells, the sounds of the crumbling buildings.
Juliette is a main character. She has a special power that she has to deal with in this dystopian world. Adam is also important. He has a connection with Juliette and they go through a lot together. Warner is another key character. He's complex, being both a villain and someone with his own motives and desires.
Well, in 'Shatter Me' dystopian novels, there's a sense of isolation for the main character. Juliette is isolated because of her power which she can't fully control. The novels also have a lot of action - there are battles and struggles against the oppressors. And the way the future is envisioned, with limited resources and a lot of fear among the people, is a typical feature of dystopian novels.
In these novels, Warner is a very important character. He has his own motives and his character arc is quite complex. Kenji is also a main character, often providing support and comic relief in the story.