DESIGN PRINCIPLES: BALANCE

In this book by Stephen King (artwork by Tom Hallman) We can see a clear demonstration of Symmetrical balance through the mirrored buildings on either side of the "peace sign Ferris wheel thing".  We can also see symmetrical balance in the waters reflection of the aforementioned peace wheel.   If you want to get even more detailed, you could state that the peace wheel is a version of radial symmetry achieving balance through the dark mountains on the lower left of the wheel, and several dark helicopters on the top right.  The Sign (Hearts In) balances the text of the composition from the top (STEPHEN KING) through solidity.  Even though Stephen King is much bigger text, the darkness and shade of 'Hearts In' balances it out.

  (Stephen King, Hearts In Atlantis, Pocket Books Publishing, 1999)

DESIGN PRINCIPLES: UNITY

In this book by Steve Cash (artwork by David Stevenson), we can see several examples of unity.  Unity by containment is demonstrated by the mass of people sandwiched between a building and rail car, bringing them into any sort of containment can help with identifying unity.  Unity by repetition is shown more than once, in the wires hanging, the suspended lights, the people themselves, and the same text that is used in the words 'Time Dancers' and 'Book Two of The Meq".   Unity by Proximity is applied to the people, creating a high amount of visual tension.  Finally, unity by Continuity  is shown with the people fading into the background from a single frontal point, and the lights continuing into the background in the same manner the people do. 
(David Stevenson, Time Dancers, Del Rey Trade Paperback, 2006)