If you have a single good character that could be the driving force of your story. So how do you create a good character?
First think of the characters you admire. They could be characters you have watched on TV or read about in books. They could be characters in novels you have read or epics and folklore you have read and heard as a child. They could be the people you have met in your life time or people you have invented from scratch.
A character has certain physical traits. You must have learned how to write a character sketch in school when you had to learn how to use your adjectives. So you already know that your character has physical traits, facial expression, specific voice, etc. Some writers create a list of characters and outline all their characteristics before they begin writing.
Before you design your character, you have to know the genre of the book you are writing. If the book is a fantasy, you can be more adventurous about your characters- they could fly or change shape, but if your book is set in a middle class suburb in Bangalore, the characters need to look like contemporary Bangaloreans.
There is no limit on the number of characters you can have, though it is sensible to have as many characters as you can be true to. The Mahabharata is successful inspire of the enormous number of characters that take the stage. If you know how to bring out specific traits for each character successfully and if your character has an important role, not to mention a nice-sounding name, he will steal the show. Even after so many centuries Shakuni is a character that every Indian who has some knowledge of the Mahabharata can talk about.
So why do we remember Shakuni? Because of his wily ways and fondness of deception and trickery. We know this about Shakuni more by what he does than what he says. When you write a character, you do not say that the man was deceptive and fraudulent; you show how he makes fools of others and this action becomes part of the plot as well.
Who is your favorite character of all time?
Some more links on how to write characters effectively: