That's a huge question but not that difficult to answer. Number one, you have to want to tell a story. Doesn't matter the genre, or the setting. Number two, you need to keep the audience involved.
You also need to know the basics of grammar and punctuation. Strunk and Whites The Elements of Style is here in a free ebook http://www.bartleby.com/141/
You need to use plotting that carries the drama forward rather than sidetrack with things that don't keep the main idea foremost: Ex: In Alice in Wonderland we follow Alice's adventures. We aren't drawn away by what her sister is doing or what the cat Dinah gets after. Lewis Carrol sticks with Alice and her activities, her thoughts.
You need to know the difference between Show and Tell. Today the emphasis is more on Show 80/20 to Tell
Tell is visual with few details that connect: He was afraid.
Show involves the senses, emotions and thoughts: His knees shook, the blood pounded in his veins, his face went white and a sour taste rose in his throat.
15ish years ago I had a wet cold marvelous afternoon, despite a massive migraine, being a character in a live action role play. That choreographed plot led to me writing a story about it, then adding my friends' characters, then switching to another online RP, then making up more characters and having adventures beyond that.
I'm into the 4th book, editing the 1st and will do the same for 2 & 3 with only my original characters and situations in the series.
It all started with 'what if there's this woman with scales on her left side' then there's how that happened, her family, her upbringing, her friends, her enemies, her loves and hates, what's happening in the larger world, what ties things together, and on and on.
Everyone has a past, a present and a future. No matter the genre here's always more to write about the person, the climate, culture, the civilization, the cuisine. Stories end at some point but the characters have children, friends, enemies, their actions which set another plot going.
So you write, and rewrite, and carry a small notebook with you for ideas, and have one in the toilet, in the living room, by the bed, in the car, because ideas are and do come from everywhere. Just write them down.