SFX magazine asked Eoin Colfer (the Artemis Fowler novels) the secret of getting started as a writer. He said, "Like an profession, you gotta keep doing it. You're not gonna be a writer if you write just two pages a year. You'll know people who are saying 'Oh yeah, I'm writing a book!" And they're basically talking about writing a book."
He adds, "Try to bring something of yourself to the book rather than take everything from your favorite author...A good way to do that is in every story you write tell yourself, 'Now I'm gonna put one thing in this that I've never heard anywhere before.'
The tip I would add is take it step by step, day by day. At the start, the size of your dream dwarfs the tiny bit you can do to move toward it today. But if you keep going and keep adding those pages, eventually the reality will be as big as the dream. Along with that, don't be hard on yourself when what you write doesn't live up to what you'd hoped to write. It never does, but there's time later for rewriting so that it will at least get closer.
(You need support and you need to manage your time well if you want to get started as a writer. My online mentoring program can help. To get information about it, as well as my free report on "Seven Things that Are Stopping You From Writing--and How to Overcome Them" go here: http://goo.gl/bWjb.