Something I distinctively remember from the movie Oblivion (2013) was the co-pilot character Vika. As the story told, Vika and Jack were cloned, many many times, to create mechanics to run sci-fi machines. They were copies, without memories. Vika would appear perfectly bland and colorless if it weren't for a beautiful detail that the script placed in the story for her character: her favorite little phrase "Another day in paradise." She said it before the cloning ever took place, and she continued to say it after. It gave a little window into her personality, proof that there really was a person inside. Real emotions. Real quirks. Her phrase let us know that she was still, well, her. It reminds me that, no matter how small a part your supporting character has, he/she needs details in their character design that separate them from the crowd – even if they are a clone.