Believe in your story: in order to give your story a voice and bring it alive, you must first believe in your own story. If you don't then you'll have difficulty trying to put words on paper for fear that no one else will believe it.
Believe your story is worth telling: Every story is worth telling, and every story has its reader. So know that once your story is told, it will find its audience. You just have to give them something.
Reading is key: Read for inspiration. Read for style and voice. Read for lessons - to know what you like and don't like. Then find your own unique voice and own it.
Pay attention to that tug: Don't ignore that yearning tugging on your heartstrings. It is the one voice you must listen to.
Just write: If all else fails, just sit down and write a starter sentence. You'll be amazed at how the story will flow from there.
Write everyday: Once you get started, be sure to add a little to the story everyday. Then be sure to stick to it until you have a final draft.
If all else fails, seek outside help. A writing coach can help you get started, and a ghostwriter can help you write if you feel you have the right story but not the right skills to get it in print.