It’s stating the obvious to say that the characters are the most important element of a story. But most writers, particularly beginners, don’t spend enough time designing the population of their book, and the result is lukewarm fiction.
Remember that your protagonist can only be as strong as your antagonist, and that plot is conflict.
Remember that if you don’t spend time designing your characters, they will all sound and act like you.
Remember that fictional characters are all a little bit larger than life. By this I mean that your protagonist will have his good qualities exaggerated a little bit, and your antagonist will have his evil qualities exaggerated a little bit. But nobody is all good or all bad, except cartoon characters, so every one of those you choose to act out your message must be well-rounded personalities.
One handy tool for character development is the list of the Seven Deadly Sins: anger, greed, gluttony, envy, pride, lust and sloth. On the other side of this are the Seven Principal Virtues: prudence, courage, justice, self-control, faith, hope and charity. Mix and match these qualities in every one of your characters.
Pay attention to their names. Don’t burden your book with nondescript names like Bill, Bob, Joe, Tim, Stan, Debbie, Jane, Betty and Linda. Think Clarice Starling and Hannibal Lecter. Think Jim Nightshade, Scarlett O’Hara, Rhett Butler, Count Dracula, Major Major, Victor Frankenstein, Mary Poppins, Peter Pan.
Take every opportunity to reveal your characters’ insides. Show their hands. Hands tell a lot about a person. Show your readers how your characters react to children and animals. Show your readers the inside of your character’s refrigerator. Is his house filled with lush, thriving houseplants or is there one dead cactus on the windowsill? Give your characters guilts, pet peeves, irritants, quirks and physical oddities. Know their backgrounds and their (hopefully quirky and memorable) families in great detail. If you believe in astrology, know your characters’ signs, and their siblings’ signs and how they relate with each other.
But most importantly, reveal your characters’ emotions, for it is through their emotions that your message is conveyed to the reader. Remember that your protagonists are usually unlikely heroes. Fiction is about people in trouble. We all react strongly when trouble is visited upon us. When you think about “writing what you know,” instead of thinking about your mundane life, think love, hate, anger, joy, grief, disappointment and triumph. Your characters may live in a different time or be of an alien race, but they will have human emotions, and your readers will resonate with that.
For an extraordinary trip through a character’s development and emotional content, read Gone With the Wind by Margaret Mitchell. There’s a reason this book is a classic, and if it’s been over ten years since you’ve read it, it’s time to revisit it. Read Watership Down by Richard Adams for an example of superb writing with non-humans as the characters. Invest in a good book of names and their meanings. And for a great reference tool for fictional relationships, Linda Goodman’s Love Signs can’t be beat.