Start or join a writers group. You will need the support and suggestions a group of like-minded aspiring writers can provide. Writers groups sometimes meet weekly, and members read and offer suggestions on each others' works in progress. Inquire at your local library, look at community bulletin boards or on-line forums, or perhaps read postings at your local book store. If you want to start a group, try posting a message at any of these forums.
Keep a notebook with you and write down ideas for characters, stories and plot twists as they occur to you. Oftentimes, inspiration will strike when you are not focused on your writing projects. Ordinary occurrences can take on a greater importance when you see connections between your day-to-day life and the story that you have been wrestling with. Write them down, and review them later.
Choose the characters you want to write about. Give them names and family histories, if they are purely fictional. If your characters are based on real people you have observed, you might want to rename them. Allow yourself to daydream about how your characters will interact, what they will have in common and what conflicts they will experience to get your stories moving. Make notes on how your characters will react to and deal with conflict, and how they will resolve their problems, or perhaps fail to resolve them.
Outline your stories before you begin writing. Some writers prefer to begin with a simple notion of what they want to write about and expand on that original idea as the project begins to unfold. Most novice writers will benefit from planning ahead before writing. Outline your short stories, and then create another outline that maps out how the short stories might fit together to form the basis for a novel. Complete your long outline, then go over it again and add more detail until you're satisfied with the direction your novel will take.
Begin writing, and use your outlines as guidance. Do not, however, cling to the outlined path you have established for your stories if a stronger idea occurs to you. Be flexible and open to unexpected twists your story may take. Likewise, use your short stories as a guide to how your novel will unfold, but do not insist on remaining completely consistent with the work you have done in short stories. Finish your novel as quickly as possible. Give yourself some time off, and then read and rewrite it as needed.