Giving yourself ideas (and remembering them!)
I expose myself to a lot of really good stories. I watch films, read books, read comics, watch TV series, listen to audio books, read the news, and hear a lot of really good ideas for stories in my roleplaying game.
Copying isn’t bad
Taking a story that you’ve heard before and using it isn’t bad. There are many ways you can take an idea and use it as a story which is totally legitimate, and might be totally different to the original story that inspired you. Most works of fiction are inspired by other works of fiction. Taking a good idea that you’ve heard and applying it to your own characters might create a very different story.
There are many interesting background stories or settings that you could use, and adding your own characters into the story will create a very different story, and could have a dramatically different outcome.