(It's often more interesting if the antagonist has a goal seperate from merely the opposite of what the protagonist wants.)
How to Use:
1. Roll yourself up and get a goal for your Protag. What are they pursuing this novel/chapter/scene? Some of these are super broad and some are weirdly specific.
2. You can be done if you like, but why not make your Protag's goal a little more complicated? In order to accomplish Goal One they must first accomplish...GOAL TWO.
3. If you got yourself a longer story, give your Antag a goal as well. It doesn't have to simply be that they're a wee contrary butt. They can want things unrelated to your pesky Protag.
I like to use this in conjunction with the two most helpful story generators I've seen: Cool Bits by Telophase for inspiration and Random Plot Points for bad things to get in your character's way.
Thanks to Sophanarith Sok for his article on how to make a simple generator.