Write a short story. During the writing process, keep in mind the basics of good story wring. A good formula is to begin with action, then go to background information. Next you will need dialog and description to develop your story towards a climax. Finally there is the ending. Remember that the ending can be subtle, while the climax is usually not.
Develop a style of your own. This comes with time and practice. Style is all about how you will use grammar and dialog. The best results are when you find a happy medium that straddles the two extremes of perfect grammar and honest dialog. The more you write, the easier it will be to develop your own style of writing.
Let your stories add up. Don't write just the number that you need, but instead write lots and lots of stories. Once you have collected a large assortment of stories you will need to decide, which ones to include in your manuscript. There are different criteria that you can use to do this. You might want to select stories that take place in the same place or time, or you can use theme as a way of choosing your stories. Making an outline can be a very big help at this juncture. When you list everything out, it will become easier to make the final decision.
Go back and "tweak" a story if you have to. You may want to change a small item, such as a character's name or overall setting of the tale. You can also make bigger changes, such as switching from a first person to a third person narrator.
Push the book into a novel form. The borderline between a collection of short stories and a novel can be very thin. Two excellent books that straddle this line are "Tales of the South Pacific" by James Michener and Tim O'Brien's "The Things They Carried." Reading these two books will reveal wonderful insights into this dichotomy, as well as give you some good entertainment.