What makes your readers love your main character and hate your protagonist? It’s the classic Good vs. Evil scenario. When you create a main character readers empathize with and an antagonist who is really bad news, they will root for the good guy to win every time.
You want your readers to feel strong emotions about your characters, one way or another. Think about a storyline that starts off with the protagonist as a somewhat unlikeable character or doing bad things. Then, throughout the story, it becomes clear why the main character had to do those bad things and we sympathize with him or her.
Now consider a story where both the protagonist and antagonist are both sympathetic throughout. If you can carefully tread to make your readers like both characters, you'll tear their emotions at the end as they agonize over who should win. According to Orson Scott Card, this situation causes "anguish, perhaps the strongest of emotions you can make your audience experience directly (as opposed to sympathetically mirroring what your characters feel)." Because really, it comes down to moral issues that one should prevail. And you can’t guarantee that your readers will agree with your outcome, but they will definitely care more about it.
This is why you shouldn’t give your protagonist all likable qualities. He needs to have flaws, and the same goes with your antagonist. She can’t be completely evil if you want an authentic character. Card also says, "The true 'antihero' is rare in fiction. Most seeming anti-heroes are really heroes who need, metaphorically speaking, a bath."
The key is to learn how to create sympathy or antipathy towards your characters. How do you do that?
Give the right first impression
We like characters most like us, right? Maybe they belong to the same community or are the same age as us. Maybe they dress similarly to us or appear to be of the same economic class. The truth is that we’re most comfortable approaching strangers who are more like us.
Whether we want to admit it, when others dress wildly different from us or behave outrageously (something we would never do), we dislike them and don’t trust them. We avoid them.
So basically, your readers want characters they can easily pinpoint as being "like" them or "unlike" them. Then add to that a bit of the opposite, because opposites attract. This will help you create characters who might not give off a great first impression but will win readers’ sympathy as the story unfolds.
Finally, add a dash of the strange to pique your readers’ curiosity. Make your protagonist intriguing and a little different.
Make readers love ’em
If you want your readers to fall in love with your protagonist, give him or her the following characteristics:
Physical attractiveness. The physically beautiful attract us, whether or not we want to admit it. That’s why so many writers describe heroes and heroines in terms of great physical attractiveness. Some authors create protagonists without ever really describing what they look like. This allows readers to see themselves in the character. But be aware that physical attractiveness in and of itself will not create sympathy for your character. They need some flaws as well.
Altruism. Orson Scott Card says you must make characters who are "victim, savior, or sacrifice." Consider the female protagonist who is a victim of abuse. There is a fine line to creating a character who inspires sympathy and one who seems weak and a little contemptuous. You must show readers the viable reason she doesn’t just leave her abuser. The "savior" must come across as humble, someone who only wants to help someone else out of a bad situation. Otherwise, he or she looks like a meddler. And finally, when your character sacrifices himself, you must convince your readers he is willing to suffer or even die for something that’s right or important. The sacrifice must make a difference. Or show your character doesn’t have much of a choice.
Purpose and pressure. You can’t have a main character who does nothing but react to something that happens to him or her. Your audience won’t sympathize, and they’ll wonder why he has no initiative. Give him or her a purpose; in fact, there should be several purposes. Maybe your main character is worrying about a lump she found and her teenager’s teacher wants to speak to her about recent behavior issues. Then her boss gives her a serious assignment that takes her away from home for weeks at a time. Increase the pressure on your characters and you’ll increase your readers’ sympathy.
Courage. Your protagonist can do nothing sneaky or underhand. You’ll lose readers’ sympathy if she gloats when her rival fails or cheats to win in the end. This doesn’t necessarily mean your main character always have to be courageous, but you might lose a little sympathy if she’s not.
Attitude & dependability. Does your main character whine when bad things happen? Does he try to pass the blame or shift responsibility onto someone else? If so, your readers won't like him for very long. Your protagonist should never brag about his good deeds or be unwilling to trust others. His word should be golden, too. Never let him intentionally go back on his promises. Your other characters might not see how "good" your protagonist is, but your audience should always recognize those qualities.
Smart, not intelligent. Readers love characters who are clever enough to figure out how to get out of situations, but not an intellectual type who lords his intelligence over others. For example, your protagonist must never point out or notice how clever she is when she comes up with a plan.
Flaws. Finally, your protagonist needs some endearing flaws to help readers see him or her as human. You need to balance your character traits between those that are believable and those readers care about. Consider all the main characters that are unforgettable. They all have flaws in some shape or form.
Make readers hate ’em
Actually, getting your readers to hate a character is easier than winning their sympathy. And the more loathsome, the more memorable he or she will be.
Bully. Everyone hates a bully, especially a sadistic one. An antagonist who constantly torments or tortures the main character will cause readers to hate them. The bully becomes the "evil" that we all hate in others because of their love of power and control over other people. And readers hate to feel powerless or not in control.
Assassin. Your antagonist can’t assassinate someone who deserves it. If your character is trying to assassinate Hitler, for example, you will more than likely create sympathy for his goal. Rather, he needs to murder to increase his power and control over others. Murder must only be for selfish reasons and must only hurt those who don’t deserve it.
Self-centered. Readers hate an antagonist who is only interested in what’s best for him or self-appoints himself as the "savior" for reasons of ill-gotten gain. Show your character as willing to do anything to anyone to move up the corporate ladder. Or show her trying to worm her way into a situation where she wasn’t invited.
Untrustworthy. Your antagonist must be untrustworthy, too. Have him or her break an oath to the protagonist, and you’ve created a love/hate relationship between them. When a character breaks an oath or betrays someone else’s trust, readers know they’re not a nice guy.
Intelligent or insane. Creating an antagonist who flaunts his intelligence over his victims causes readers to hate him or her. And insanity pushes the envelope even further. The psychopath and sociopath both repel readers’ sympathies. But like Hannibal Lecter, they’re unforgettable characters.
Attitude. Create an antagonist with an attitude problem. Perhaps he always whines or complain. Maybe she has no sense of humor. And they should show no regard for others’ feelings or needs.
Redeeming qualities. Finally, give your antagonist some redeeming qualities. You don’t need or want completely evil villains. You want complicated characters who compel readers to feel a bit of sympathy and remorse for what happens to them. But just a little.
Consider creating an antagonist readers will pity more than hate or fear at the end. And create a protagonist who is unassuming and humble when he/she emerges victorious.