Juxtaposition is a strong tool you can use to create imagery and emotion. It occurs when two things that shouldn't usually go together are placed side by side for comparison. For example, seeing children playing and running through a war-torn village, amongst rubble and death. Children and Death are two themes we don't expect to see together.
I use this writing technique when teaching English for assignments such as creation a visual representation of a poem. Using a poem about the vietnam war, a student showed children on swings and the next slide was of dead young soldiers. The image was made stronger because we were reminded that those dead soldiers were once just kids on swings. Even though the two images seem totally unconnected, we find a connection. That's what people do, we look for connections.
Cinderella appears even more beautiful and sweet because she is contrasted with her wicked ugly step-sisters. But rather than have such black and white juxtapositions, make good and evil exist within the one character. Seeing your bad guy condemn a prisoner to death and then buy his little girl a pony shows a contrast of personalities within the one character.
If your theme is loyalty, you'll want to contrast it by showing betrayal. If it's bravery, show cowardice. And try to show new ways of placing these themes together, rather than the old one bad guy, one good guy. Mix it up.