It's important as a fiction writer to understand the differences between novels and short stories. For short stories, no word can be wasted by the author. They must be concise and focus on giving the reader a single emotional impact. Novels use large-scale plot structures, and can even have several different plots going on at once. Generally speaking, it is a good idea for authors to begin by writing short stories. The discipline learned will act as a building block for the creation and publication of an author's first novel.
When writing fiction, you are your own boss. It's important to be intentional about getting things done and being productive every day. Creating a weekly schedule and word quota will allow you to clearly assess how much work you're getting done per week. For many authors, writing around 350 words a day is a good starting amount. Some days your words will flow onto the page, while others you may need to struggle for each sentence. No matter the day, follow your schedule and make sure you're reaching your word quota.
The best way to get better at writing fiction is to read fiction. Reading through the classics and great works will help an author improve their own writing. It is also important for each author to read the genre they will be writing in. Like an athlete who watches his sport, a writer should read his genre. Doing this helps the author to avoid clichés, find new ideas and see what great writers have done for a particular genre already.
When you start writing your stories, be sure to keep writing till they're finished. It can be a tempting habit for many beginning authors to write a few sentences, then stop and correct any mistakes they find. Doing this disrupts your train of thought, and can douse creativity. Making a habit of writing out a story or chapter completely is a good idea. If there is a point when you feel like a page will need serious editing, make a note of it and continue on.
Keeping a notebook for brainstorming is beneficial for any writer. Chances are your ideas won't all come when you sit down to write. They will probably appear throughout the day. Write whatever comes to mind for referencing later on. It can be anything from a simple quote to an idea for a scene. Journaling gives an author ideas he or she can use for brainstorming or as inspiration for future fictional works.