Research the books being published today for children as well as the classics to get a feel for what's already been done and what's popular. Read literature for the age group for which you want to write. If you're interested in writing picture books, for example, read authors such as Margie Palatini and Judith Viorst. If you want to write for a mid-grade readership (ages 9 to 12), then read Neil Gaiman and Lois Lowry. Writers of young adult literature will want to read popular authors of teen novels, including Meg Cabot and Eoin Colfer. Browse bookstores to see the currently popular children's authors.
Choose a setting. Research your setting to make sure details are accurate. Avoid assuming that detailed research isn't needed in children's literature. Although your descriptions may not be as detailed in children's stories, the standards for research are more stringent for books written for kids.
Learn your market. Chances are, kids today have different attitudes and lifestyles than they did when you were a kid. Talk to children you know or read magazines and websites aimed at kids to get a feel for the issues they face, their taste and the language they use.
Write to your market. Children's literature is organized not just by genres such as fantasy, paranormal, science fiction, romance, mystery and drama, but by age groups. Age groups often overlap. Decide if you are writing picture books to be read to very young children, picture books and chapter books for children under eight, mid-grade children's literature (aimed for kids 9 to 12), or young adult or teen literature, for ages 12 and over. Alter your vocabulary to the comfort zone of the age group you're writing for, but be careful not to "dumb down" your language. If you've a choice between using the perfect word and using a word that may be a little too advanced for your reader, use the perfect word.
Choose a plot that's rich in the kind of conflict that appeals to children. Think about your own childhood and children you know and what they like. Even with changing attitudes, today's children will be drawn to the same essential core plots. Plots that involve danger, suspense, mystery, romance, issues pertinent to growing up, and issues about living in today's complex world are all viable.
Create your hero or heroine, also called the protagonist, as well as minor characters. Make your characters believable. Give your protagonist both likable qualities and flaws. Construct a rich personal history for each of your main characters.
Write a story with plenty of dialogue and minimal description to keep the pace fast. Write children's literature in a style that's concise and easy to read. Smooth out any rough areas of prose. Even more than in literature written for adults, there's no room for extraneous words or awkward sentence construction. Kids don't have the patience to read "filler."
Do include experimental techniques, fun variations on the tried-and-true methods of telling a story. Children enjoy innovation and have few prejudices about the way a story is supposed to be told. Always, always entertain.
Join the Society of Children's Book Writers and Illustrators to learn about markets for children's literature, form connections to get critiques and discover other children's writing resources. (See Resources for the link.)