When you pick up a short story, you may only be in their world a short while, but it still needs to feel worth your time to meet these people, even in passing. So, how do writers create characters who are compelling enough for readers to care about?
1. Get to know your characters, inside and out. Physical descriptions are helpful, but it's not quite enough to just describe what your main character looks like. Your reader needs to know who s/he is, inside. What does s/he like? What is s/he afraid of? What does s/he want most, deep down in his or her heart? Who are his or her friends?
This is true for actions (and reactions) as well. For example, what if I held up a red apple in a roomful of people? A hungry person might lick her lips and lean forward. A fearful person might raise up his arms as if I'm going to throw it. A person who just failed her driver's license test might flash back to the red stoplight she almost ran. And so on.
4. Celebrate your characters' imperfections. No one is perfect. Sometimes we write down our fantasy characters, giving them all the best characteristics we can imagine--we make them courageous, good looking, honorable, talented, self-confident and more. Don't forget It's okay for literary characters to be larger than life, but not flawless. Readers won't believe your character is flawless. Plus, a character without a weakness or two is not going to be able to grow and change and make us worry if s/he will survive.
5. Give your characters unique challenges to overcome. Let who your character is determine what his or her story is going to be. Lots of books are written about romance, for example, yet no two romances are exactly the same because the personalities of the characters give each story a special flavor. Your character may face problems that many other people have faced before him or her--but how s/he responds to those challenges is what makes your story interesting and different.