Perhaps Barbara Kingsolver is best known for several aspects of her writing. While she portrays her characters with humor, as well as her plots, and though there is a certain sense of the unusual even quirky about her characters and stories, there is also a strong sense of purpose and thematic development in her novels. 

In The Bean Trees, Taylor Greer leaves home and drives as far as her car can carry her, to leave her hometown behind so she doesn't end up pregnant and stuck there for the rest of her life—like so many of her classmates.

Kingsolver's characters are quirky and unusual. Newt Hardbine, for instance, is...

...one of the big boys who had failed every grade at least once and so was practically going on twenty in the sixth grade.

Mattie, one of the first people Taylor meets when she moves into town, owns Jesus is Lord Used Tires. She welcomes Taylor and they become good friends. There is a great deal of plant imagery in the story; in addition to selling used tires, the unconventional Mattie has...

...a bright, wild wonderland of flowers and vegetables and auto parts.

Kingsolver's sense of humor is apparent. However, Taylor's character also has to deal with deeply serious issues. She adopts an abandoned Cherokee toddler, given to her (Taylor assumes) by the child's aunt who fears for her safety because "Turtle" has been abused. 

Taylor also deals with the threat of predators to children when a man attacks Turtle in the park when she is there with Edna (who is blind). Edna swings her cane hard (avoiding Turtle) and hits the man, who runs off, leaving Turtle traumatized for the experience...but physically unharmed. For Estevan and Esperanza, Taylor learns the truth about people who stand up to tryannical governments and must flee for their lives—leaving a child behind—to build a new life in a new country. 

[Kingsolver's] stories typically address contemporary social and political evils, from poverty and child abuse to...human rights violations.

The author portrays strong female characters: most of the people in her stories are women who are finding ways to survive on their own, in good part by relying on (and supporting) each other.

A literary technique is something the author uses to get his or her message across to the reader in the most effective way possible. There are many techniques ("devices") Kingsolver uses, but if I had to identify one that she uses which makes her writing so effective and noteworthy, it would be her "writer's voice," which can also be called her writing "style."

Voice was generally considered to be a combination of a writer's use of syntax, diction, punctuation, character development, dialogue, etc.

Aspects of her voice that stand out the most for me are her character development and dialogue. Using these (and other) literary techniques, Kingsolver engages the reader so he/she cares about the novel's characters, but is also able to see humor in life even as her characters face some dire situations. Kingsolver's "voice" is unique and compelling.

Her voice is evident at the end of The Bean Trees when Taylor explains to Turtle that they are now a real family—use of "kid" and "nobody" instead of "daughter" and "no one" are specific to how the author presents Taylor:

"That means you're my kid," I explained, "and I'm your mother, and nobody can say it isn't so. I'll keep [the adoption certificate] for you till you're older, but it's yours. So you'll always know who you are."