Characters, aside from villains, should be lovable, or at least likable. Never perfect. Your characters must have flaws for readers to be able to empathize with them. Remember Emma Bovary in Flaubert's Madame Bovary, Dashiell Hammett's Sam Spade and Helen Fielding's Bridget Jones?
The most important thing to remember is to focus on your character's vulnerabilities, according to writing instructor Bret Anthony Johnston."Your focus can be on physical or emotional vulnerability, but it has to be intimately tied to the character. What makes her sad, embarrasses her? What frightens her, what does she regret? What minor or major trespasses has she committed?"
In the case of Emma Bovary, we can sympathize with her mistakes and how they affect her life.
What does your character need or want? And what does he stand to gain or lose by the conclusion of the plot? Whether or not the character achieves his goal isn't as important as how badly he wants it. Your reader will hang in there with your protagonist once she understands his goals and desires. Make that desire as compelling as possible. A character who wants to achieve world peace is far less desirable, according to Johnston, than someone who craves a gourmet dinner, because the goal is attainable.
Once you decide what it is your protagonist wants, emphasize it throughout the story. From the first paragraph, your reader should understand the character's goal and it should color everything he does. And the more he wants something, the more the reader likes him.
Dialogue is a great way to portray a character's weakness. If he talks about someone else, the reader picks up information about the character himself by his description. The type of food he eats or the genre of music he listens to gives us some insight into his character. Does he stop by a fast food place for a burger instead of a restaurant for a good meal? Does he smoke a pack of cigarettes while on stakeout?
In The Great Gatsby when Nick Caraway tries to describe how Daisy Buchannan speaks, he says, "Her voice is full of money." Fitzgerald's few words tells us a lot about both Caraway and Buchannan.
A writer's job is should be more like a method actor than a news reporter. Striving to see the world through your protagonist's eyes is most important. Focus on the details and events happening in his or her life. But that doesn't mean that your fictional characters should like the same things you do or share the same views. Nor should they become your parrot. Each character should have his own distinct speech pattern and outlook on life.
Keep your protagonist in proverbial hot water as much as possible. Allow the water to cool periodically to avoid melodrama, but keep turning up the heat until events come to a boil. When your character has achieved his goal or solved his dilemma, remove him from the pot and dry him off for a satisfying ending.