Writers should continue to study their craft. You can join writing organizations and listen to speeches, or you can simply pick up a book and read the advice given by experts. I enjoy reading novels by Janet Evanovich (pictured above) so I picked up a copy of How I Write - Secrets of a Bestselling Author by Janet Evanovich with Ina Yalof.
In the section on characterization, Janet gives three tips.
1. The main character must want something.
2. Someone or something (nature, money, distance) must stand in the way of his getting what he wants.
3. The choices that a character makes in his efforts to overcome obstacles and ultimately get what he wants define the character.
For more advice, you can pick up this title in ebook, paperback, or audiobook.