Writing a big story for the first time can be very difficult. There are so many different factors that go into being able to write a long story, so here a few to help you get started.

1. Make sure you chose a good topic. Choosing a good topic is one of the most important parts of your story. If it’s a boring topic the reader won’t be intrigued and will stop reading. You have to make sure that the topic you chose is something you’ll be able to write a lot about, not something that you have one really good idea for, but when you have to write everything that happens before and after it you have no idea what to write. 
2. Making sure you give enough detail. Not giving enough detail in your story can lead to confusion for the reader and that’s never a good thing. Although you may know what’s going on in your head doesn’t mean the reader knows exactly what your thinking. Imagine you have a main character and thought the story he’s referred to as Tom, no detail about what he looks like, whether he’s young or old, there is no way for the reader to tell unless you write these things down. 
3. Find a spot where you can write. Trying to write a story in the middle of a busy and loud street, not the best choice. Writing a story in a quiet room on a nice soft couch, that’s a much better place to write. Loud noises and lots of distractions can cause you to lose your train of thought. Imagine your writing a chapter in your story and all the sudden you have a great idea for something to write, all the sudden someone walks into the room screaming about something random and you get distracted. There you are a minute later after having an Albert Einstein type thought and you got so distracted that you lost your train of thought and now have no clue what you were going to write. Don’t let this happen to you, find a good place to write. Also don’t be the guy who walks into a room that people are writing in and start shouting, it’s annoying. 
4. Try not to jump around in the plot. Jumping around in your plant can make your reader confused. If your constantly changing scenes and not saying how a person got there or when they got there it can leave the reader wondering how they got there, maybe they can teleport, all they can do is guess because you never told them. 
5. Revise your story. Revising your story is one of the most important parts of writing. Your story could be about some dude named Jack and by accident you write Jacki by accident and it autocorrects to Jackie, now to the reader you got some random character named Jackie who never gets mentioned again in the book, never a good scene. Im usually the guy who never revises their story or essay, but that’s besides the point. It’s fine if you slack of when revising a small paragraph, but if it’s a whole story, that ain’t it chief. Don’t be that guy.

     There is a lot more then five things that are important to remember when writing a story, but these are just a few things to remember when getting started.