Choose one major event from the novel and rewrite it from the perspective of a different character.
In order to write this you will need to choose both a character and an event that you would feel comfortable with. Choose an event you know well and understand. Choose a character whose point of view you feel you understand well.
Because the book is written from Scout's point of view, you will want to choose a scene that might be significant to someone else for a different reason than Scout's. For example, if you were to choose an event that was significant to both Scout and Jem for similar reasons and then told it from Jem's perspective, it would be different, but perhaps not significantly so.
An example of an event you could choose to write about from another perspective might be the mob scene from Ch. 15. In that chapter, Atticus goes to stay outside of the jail to protect Tom Robinson from what he has heard might be a group of men wanting to hurt Tom. Scout intervenes and diffuses the very tense situation. If the scene had been told from the perspective of Atticus, it would be very interesting to know how he felt sitting there. Was he scared? Was he confident? Did he have a plan if the mob showed up and were armed? What did he think about his children showing up in the midst of it and Scout jumping into the middle? All of these answers could help you to write this event from his perspective.
What's exciting about this project is that you will be able to take certain creative liberties. Boo Radley is a character who is very present in the novel even when he does not show himself, so one option would be to write one of the scenes that he is observing and make him the lead character.
Basically, you'll want to pick a scene from the book that you enjoyed that you may have more questions about, and answer those questions by putting yourself in the place of somebody else who was also in that scene.
Remember not to re-write a scene from Scout's point of view since the novel is already written that way.