If you've never really written before, I'd say start small. Like a short story, or series of them all connected. A book is a serious and grand undertaking. If you haven't the experience, there is a very good chance you'll get lost in the enormity of the project.
Writing workshops is also a good idea that was mentioned here.
And one more piece of advice was given to me that I've really taken to heart: Write because you want to. Don't force yourself. Writing, even when writing another fantasy story in the sea of them, is an art and and expression. If you're forcing yourself to write, it's like bad acting. Do what you can to get in the mood for writing (The right setting, music, whatever), but don't force it. Forcing it will only dilute the vision in your mind.
Writing workshops is also a good idea that was mentioned here.
And one more piece of advice was given to me that I've really taken to heart: Write because you want to. Don't force yourself. Writing, even when writing another fantasy story in the sea of them, is an art and and expression. If you're forcing yourself to write, it's like bad acting. Do what you can to get in the mood for writing (The right setting, music, whatever), but don't force it. Forcing it will only dilute the vision in your mind.