Many stories come from asking questions. What would happen if... Thought is free so be as wild as you like. What would happen if a whale materialised high above the planet? No, wait, someone already wrote that one.
Stories can come from extrapolation. Read the driest news article from the most serious paper, then ask yourself about the people the story implies. The people in the background.
Don't be afraid of using up all your story ideas. The more stories you tell, the faster you'll find new ideas coming to you. The world is full of stories. All we have to do is train ourselves to notice them.
Other people's lives are a great source of story ideas. Happily, people love to talk about themselves. It is their favourite subject. Be a good listener and you'll have more stories than you can write.
I have a faulty digital radio that cuts out at random, usually leaving sentences unfinished. It's exasperating at times, but perfect for a storyteller. When the radio dies, my mind jumps forward, trying to complete the story.
And I am willing to sell this faulty digital radio/story generating machine. All reasonable offers considered. Now, that gives me an idea for a story...