I agree with what a lot of these others have said, such as writing on what you know about. Even if you write fantasy you have to include things that you have experienced to make the story believable.
Don't be afraid of the blank page or how to start, how it will sound. You just have to keep putting the words on the page. Don't go back, don't tell yourself the writing sucks and don't despair.
It is a lot easier if you know what is going to happen in your story. You don't have to plan majorly, and if you get stuck, think about WHY something should happen.
Keep a notebook and while working on your story scribble down any of your thoughts, ideas, mights, maybes and could happens in your spare time.
Here's a few things other people have said: 'Nothing you write, if you ever hope to be good, will ever come out as you first hoped.' - Lilian Hellman 'For the writer of fiction there are two beautiful things about history: firstly, there is so much of it, and secondly, it is there to be borrowed.' - David McRobbie 'Publishing a novel involves three elements; a degree of talent; a lot of hard work; and a good measure of luck.' - R.A. Salvatore