First: let your reader see what’s coming when your character can not.
Let’s say that Dinah spends the book blindly trusting a person she thinks is her friend, but you, the reader, can tell from the way the author writes the backstabbing character that she is not a good person at all, and she’s just taking advantage of Dinah. This makes the reader care for Dinah; you feel sorry for her because she is too naïve to realize what the other character is doing, and you want Dinah to see what is really going on. You end up rooting for the character because you want them to rise up against whatever circumstance they don’t see coming.
Another important strategy is to make your character realize their actions are wrong, even if they keep doing what they’re doing anyway.
So your character is being bad. Rather than have them continue to do whatever bad thing they are doing without so much as a hint of regret, make the character realize that what they are doing is wrong. The character doesn’t have to stop what they’re doing as long as they have a reason for doing it; they just have to feel at least a little twinge of guilt. A reader can’t relate to a character with no feelings or conscience, which is the problem with many villains. Most people have their limits as far as what is right and wrong, and much of the population has morals, believe it or not.
And finally, what I believe to be most important: allow your readers to relate to your character.
Even if your character’s actions are questionable, allowing your readers to understand their motives will help to keep them rooting for the character. Let’s say, for example, that Wally is going to hook up with some stranger, when he obviously still has feelings for Hephzibah. Your reader might be thinking, “What the heck is Wally doing?” But if you give your character a reason to do it, if you allow your reader to relate to the feelings and thought process of your character, they will support Wally’s actions, or at least keep reading (which is a good thing
Of course, everything has exceptions. But it’s interesting to see what you can learn about writing from simply reading a story…the moral of this article? Procrastinate writing and go read more books!
