Theme is a controlling idea that permeates the work.  I always have my students look at a piece of literature and then answer the question:  ___________________ (name of work) is a story about____________________.  Go with your gut, and answer the question.  Usually, with some tweaking, you will come to an answer that satisfies.  There are always MANY possibilities if you think deeply enough about a piece of literature.  For example, Romeo and Juliet is a story about love, conflict, suicide, murder, fate, secrets, and the list goes on and on. 

Both The Chocolate War and 1984 have similar themes of control, rebelling against the established system, courage, internal conflict (what is right? what should I do, if anything, about it? what can one person do?)and many others.  After reading both pieces, trace these suggestions through the books and then brainstorm some of your own.  Good Luck!