These questions pop up again and again as I prepare students whom I tutor for end-of-year state exams. Often those exams require students to read a passage (or remember a novel or play studied in class) and identify a theme and write about it.
Where to begin? 
An article by Zach Wright, Assistant Professor of Practice, Relay Graduate School of Education, offers great suggestions in the current issue of Edutopia (see below for a hyperlink) for middle grade and high school students writing about theme.
First, Wright suggests that students think of specific pieces of literature as not being about individuals or specific events, but rather as being about big ideas (themes) such as love or revenge or prejudice.
Next, he suggests students brainstorm a list of such big ideas associated with a particular piece of literature such as To Kill a Mockingbird. Such big ideas could include parenting, prejudice, abandonment, friendship, integrity, fear, family, violence, and innocence.
Wright suggests teachers keep a list of such big ideas or themes visible in the classroom. When students read, they should transfer appropriate themes to the back inside covers of their books to create a specific list of themes for that piece of literature.
Next, he suggests students take any three of the themes—he calls them triads—and create a sentence from them. Starting the sentence with “when” gets the students going. For example, when a person’s prejudice overtakes a person’s integrity, that can lead to violence. (Mr. Cunningham has been shown to be a person of integrity early in the book, but when he shows up as part of a lynching mob, his prejudice leads him toward violence.) Or, when a child’s friendships overshadow that child’s abandonment, that child feels love. (Dill makes fast friends with Scout and Jem during the summers when he is sent away from home, letting Dill feel love). Or, when a child’s parent shows love, that display can bring security to the child. (Atticus shows love to Scout, holding her in his lap while he reads law reviews and answering her questions, leading Scout to feel secure though her mother is dead.)
Wright recommends the teacher know the literature well in order to show how unexpected triads can work and lead to gems of insight.
English Writing Teacher 
Excellent ideas. This is a way to look at literature and even scriptures so as not be caught in literalism and see bigger themes.
I like the idea of keeping notes.
This would be helpful if you write a book review later on regardless of exams.
Thanks
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