Find a way to inject random things into your process, and then incorporate them. It’s against the rules to reject them. So you’re telling a story and a partner randomly shouts the name of a thing, and you have to incorporate that into the story in a way that makes it natural, not forced.
There was a musician I heard on the radio once who spoke about his process with his band. They all wrote something based on some idea or feeling, and then they had to figure out a way to incorporate all the ideas into the piece.
If you’re doing art, you can change things by adding a different color. Or maybe turning the color wheel to select a random color. Or make yourself draw it upside down, turn it over and go with whatever is there.
Another way is to research what other people are doing, and get ideas or just copy the idea or the method. You will make it your own, and it will have nothing to do with whatever the original idea was.
This is improvisation, and in improvisation, you are performing live, in front of an audience. You can’t say no to anything, because they you’ll make a fool of yourself. You say yes and you build on it and make it stick and make sense.
Creativity is really quite easy. I don’t know why people get the idea they aren’t creative. The only way to not be creative is to refuse to let yourself think.