Well, first, think about what kind of story you want to tell. Is it a fictional adventure, a real-life event, or something else? Then, break it down into a clear beginning, middle, and end. Also, pay attention to your language and try to make it interesting and easy to follow.
Another theme is exploring the backstories of the characters more deeply. In the actual drama, there may not have been enough time to fully develop all the characters' pasts. Fanfictions can fill in those gaps, like delving into the character's family history or how they came to be the person they are in the drama.
Another place could be Wattpad. There are many Kdrama fans who post their fanfictions there. Look for the Snowdrop section or do a general search. However, the quality may vary, so you might need to sift through a bit to find the really good ones.
One great Kdrama to watch for a love story is 'Crash Landing on You'. It tells the story of a South Korean heiress who accidentally paraglides into North Korea and falls in love with a North Korean army officer. The chemistry between the lead characters is amazing, and the show beautifully depicts their journey of love across different cultures and political boundaries.
One Reddit horror story I read was about a person who moved into an old house. Strange noises started at night, like scratching on the walls. They initially thought it was rodents, but then they found deep claw marks that seemed too large for any normal animal. Every night, the noises got louder and more terrifying. Eventually, they moved out in a hurry.
There was a story on Reddit where a hiker got lost in the woods. As night fell, he started to hear inhuman screams all around him. He tried to find his way back following a stream, but then he noticed strange footprints that were not human - they were large and had long claws. He felt like he was being hunted and had to hide in a small cave until morning. It was a nightmare experience for him.