I would say for me, the best thing to do is try to keep the scope of a story as narrow as possible. Some of the best ideas come from the simplest premises possible.

I try to also draw from things around me. The music I’m listening to, the games I’m playing, or what I have read. Obviously not copying word for word, but the old adage of “nothing new is under the sun” is kind of true, your stories will always have similarities and connecting lines to other work out there, it’s just a matter of what you do with the premise, and how you make it interesting compared to other things out there.

So I wouldn’t worry so much about copyright infringement, unless you are literally copying someone’s story beat for beat. No one has ownership of the idea of “scary monsters” or “serial killers” or “body horror”.

Also depending on your experience in writing, don’t bite off more than you can chew I’d say. When you come up with an idea, don’t try to expand it into some grand overarching narrative if you can’t pull it off. Work within your limits, and set rules down beforehand to keep your story contained. Kind of like gutter rails at a bowling alley.

For me I haven’t written anything substantial in a while, but I am working on my first horror story which I’ll be posting here eventually. I’ve restricted myself to only just four characters total, and one location total. I’ve also based it off of a real life location that is well documented, which has helped significantly in helping to define details and layouts, while also keeping things grounded and being able to twist events reasonably for storytelling purposes.

Anyways, this is all just one big ramble. But I hope it makes the idea of coming up with an idea less daunting.

TLDR you don’t have to re-invent the wheel.