That's just what the answer is. I'll repeat my earlier answer, you start writing. Some of it is going to suck big time, but some of it won't and that's the writing you keep.
If you wanted to run a marathon you wouldn't just sign up and start running. Even athletes train for an upcoming race. You work up to it. Every dreary day, good or bad you get up and run. Maybe a mile at first then two and so forth, eventually you get there. Just do it, like the Nike ad says.
Really it's that easy or in some cases that hard, but you work at it hoping for the end result. A good solid story, with great characters you know inside and out.
There are so many resources to help writers- write. One I like using is called; One Page Per Day. http://www.onepageperday.com
It's a great way to keep doing what you love and stay anonymous, cause sometimes it's hard to get pass the obstacle of sharing your writing. The best part is people can request more of your stories. (Positive feedback is always a plus.)
So if it starts with an idea, what's you're idea? Tell me about it.
It was breakfast time at the Johnson's house which could only mean one thing; bacon, eggs and fresh hot biscuits with butter were waiting to be eaten. Mornings like these made Jane feel like she was back in the nineteen fifties. 
You start it. I got nothing right now. 
Now what? Where are we? what's happening? Who's there? Fill it in with your own writing!
tired from a long day at school. Her shoes untied, a tear tricked down her cheek. Obviously it had been one of those days. ( Now what happens? Join it. )