I am trying to write a story but I can't think of a subject?

Write what you know.

How about a story involving a forbidden relationship between two teenaged lovers from differing social classes set during Whiskey Rebellion?

Write about a teenage girl that has dreams that come true. She’s always trying to figure out what her dreams mean before it’s too late.

Can you think of any interesting happenings in your life lately? Maybe you can create an allegory to that event. It could even be an event you heard of.

Take an historical event and make a plausible change to one small factor. How would the outcome differ from reality?
What if the gun John Wilkes Booth used to shoot Lincoln had misfired and Lincoln lived? How would the world be different?

What about your life? Is there one thing that could have gone one way or the other but you selected one of the paths. How would you be different if you had taken the other path?

Think f the Butterfly effect and make a plasuble example.

It doesn’t have to be an earth-shattering story idea. Some of my favorite stories are about mundane events but very well written, descriptive with vivid characters.

Write about some special experience you’ve had. You can write it as it really happened, or you can “spice it up” by adding fictional elements.

One quick comment about @marinelife‘s comment. I agree, it’s good to write about what you know. But don’t be limited by that rule: write about what you imagine.

Write about a young woman who loves the physical act of writing, and where she learned to love that, and her ideas about what it means to write a story; make her ideas are really peculiar, and write down what happens when she writes stories containing peculiar ideas.

Here’s
a list of the 10 best short story collections of 2013 to give you lots of ideas about how other writers approach the genre.

An Ex-Marine that went to college after his servise to learn about stocks and gets loans money and looses it. Now he’s got to run from a certain scary group of people. Not a lot of planned out material, but there ya go.

A teenage boy one day gets suspicious of his true relationship with his parents and thinks he was adopted. He tries to talk about it with his father but he refuses to tell him about it. There is something about the father’s behavior that indicates that he is hiding something. And as the boy can tell, the father seems to be tormented by something. It seems strange, even for a police officer like him. The boy decides to find the truth…

Write something that you can relate to. Stories can be a phase of reality ( of you’re life or someone else) or completely imaginative.
I would suggest something real instead of imaginery. Write something that you’ve been through or lessons you’ve learnt in your life, probably anything that encircles ‘your’ life. Sure you can add a little imagination to it, but don’t go too overboard. I am saying this because sometimes your title and context of your story make no sense if you hover around virtually too much.

He’s a time-traveling gangster fleeing from his past (or future, depending on how you look at it). She’s a fast-talking magician’s assistant who can communicate with animals. Together, they fight crime!

Got paper?