In the writing community, much has been said about how to make a character likable and/or sympathetic. And I've written ways to do that myself, but there is one technique I've found that is one of the most impactful (in my opinion, anyway), and can often be quick.
Many writers remark that we need to put the character in unfortunate circumstances, so the audience will readily root for him. Others say that it helps if he is kind to people. And having a character be self-aware of his own weaknesses can be useful as well.
One of the most popular techniques is "pet the dog," which is also known as "save the cat." You have the character pet a dog, or save a cat, or something of the equivalent. It could be giving the homeless food or walking a neighborhood kid home from school.
If you want to make the audience dislike and be unsympathetic to the character, you use "kick the dog" or "kill the cat." You have the character hurt someone who doesn't deserve it. It could be a homeless person. Or it could be a child. Or something else.
My technique is a mash-up of the two, believe it or not. I call it, "feeding the dog, poison."
I know, it doesn't sound very sympathetic, so let me explain how it works.
