If you want to write a novel/novella/short story you should always start with a seed. If you ever catch yourself asking a question that starts with "What if...." be sure to write it down. Those questions could lead to a great work of fiction one day. But be careful, you don't want to start a story with too much baggage since it could limit your creativity in the writing process. You may have some idea where you want the story to go, but don't create too many constraints for yourself! The story will unfold if you are ready to work hard on keeping up with what it has to say.
When you sit down to start your story, let it write itself and be sure to keep your characters and dialogue realistic. This is accomplished through many different approaches. As a writer, you must learn to hone your powers of observation and watch people and how they interact. Research can come in a variety of forms, from reading other authors to watching movies as well. Keen observation skills and personal experience will help guide you through this aspect of fiction writing, so don't be afraid to go out and do some people watching!
When you're ready to get down to business, find a place where you can go to tune the rest of the world out. If you are planning on writing a long work of fiction, you will essentially be "living in the story." Be prepared to shut yourself in as you work on bringing your tale to life. Set aside a little time each day to write, even if it isn't on your fiction story. As they say, practice makes perfect and you won't get any better if you don't practice your writing.
One of the biggest mistakes aspiring authors make is getting caught up in the past. Keep pushing forward without taking time to go back and reread. The time for reading what you have written will come, and that's when you can fix any inconsistencies. Keep writing and worry about the minute details during the revision process.
If you find yourself caught up with writers block spend an hour or two reading. Reading other works of fiction will help inspire you and help you to become a better author.
An underlying cause of writers block could be lack of your character development. If you feel that your characters need to become more in depth try keeping a character journal. Take 20 minutes each day to get inside your characters head and write a journal from their point of view. It's a great way to understand a character and find his or her voice, and who knows, some of the entries could make it into your story.
When you feel your story has come to a close, put it away. Get it out of your sight and try your best not to revisit the work while the story is fresh in your mind. Putting some distance between writing and editing will do you and your story some good. A good way to do this is to get started on something new right away. This will help you to come back with a new perspective and keep your productivity level high in the process.
After some time has passed, print your first project out into a manuscript and read it with fresh eyes. Have a colored pen handy to take notes on the pages, chances are that you will come up with ways to improve upon and revise the story to make it flow more smoothly. The revision process will be time consuming, but it will help out when you're ready to share your work with another reader for their opinion. Don't be afraid to cut entire scenes or even chapters, but make sure that you keep copies of everything you cut. Just because it doesn't work for that story, doesn't mean it won't work in a different one.