Being predictable is great if you're talking about public transportation. Not so great for stories. Predictable stories have plots that readers can easily guess because they've seen other ones just like it over and over. For example, the unpopular girl pines for the popular boy, who is going out with a not-very-nice popular girl, but then they get put on a school project together and the boy starts to see what a great person the unpopular girl is and starts to fall for her.

I've lost count how many movies I've seen this plot in. That doesn't mean you can't write a similar story. It just means you need to add a few twists to make it less predictable.

Before you can fix a story's predictability, you have to recognize the cliches first. If you read a lot, you'll be able to recognize these. If you don't read much, you'll have to rely on what people tell you because your own experiences are so limited. Everything might seem new to you. This is another argument to read other books as much as you can.

In my plot example above, all the things I pointed out are overused, making the story predictable. The main character tends to be undesirable in some way, typically a nerd. And everyone seems to worship the guy, who could have any girl he wants but somehow has a mean, snotty girlfriend. We've seen these scenarios so often, it's hard not to roll our eyes at them.

Once you've identified the cliches, figure out a way to change it to something unexpected. Maybe the unpopular girl has the hots for the boy's girlfriend instead. Or maybe the girlfriend is actually really nice, and ends up befriending the unpopular girl. Or the popular boy could be a murderer. Or instead of a school project, they're actually picked for a mission to Mars.

You don't have to subvert every cliche. Though cliches are overused plot devices, people still read them because they like them. It's just nice to throw in something unexpected to keep readers from getting bored. That's how stories stand out.