David Kerisey has studied personalites for over 20 years. In his book Please Understand Me, he lists four basic temperments with four subgroups under each one. The four main temperments are: Guardian, Artisan, Rational, and Idealist.
I’m currently using the techniques from his book to help me develop the personalities of my novel characters. In some instances, I’m even filling out the Temperment Sorter as if I’m the character with their particular traits and answers.
For me as a writer, I know my characters to an extent, but this type of analysis helps me learn about them in more detail – beyond the obvious. It also assists with consistency in characterization. Have you ever had a character change personalities in a novel draft? This type of systematic planning decreases that possibility and should give more emotional appeal to your writing.