It's unfortunate when I feel rushed and have to start writing even though there hasn't been enough time to think about this idea. I'm currently in that situation; I should be handing in work soon, so yesterday I reluctantly started on a story that clearly isn't ready to see the light of day. I felt myself mentally dragging my feet with every word, which doesn't lend itself to the most graceful and sinuous prose. While it's good to get back into the swing of things, I really think this story could benefit from more cogitating time.
When you get your next story idea, you might consider a similar thing. While it's true that it can be good to strike while the iron is hot, I'm a strong supporter of the "step away" method. That doesn't mean I think you should plan out everything beforehand, or be taking copious notes and drawing diagrams. Instead, I think you should just know that that idea is in the back of your mind. As you go about your day, think about if what you are experiencing now would enrich your story idea if you added it in. Consider something you see on the street: would that be an interesting image to include? Details like this will make your first real writing effort much more vibrant and also more coherent, because you're bringing the experience of a real person (yourself) to an abstract idea.
I vividly remember a writing class I attended when I was fourteen or fifteen, when a visiting writing teacher gave us a haunting walkthrough of a moment in Toni Morrison's novel Sula. In this emotionally weighty moment, one of the larger climaxes in the book, a woman walks in on her husband having an affair with another woman. She is standing in the doorway, taking in the scene in just a moment, and Morrison does not linger on the tumultuous emotions and grand ideas sure to be surging through the scene. She does not give us a treatise on betrayal or discuss the theory of the marriage contract or of love. She does not even say outright what heavy emotions people are feeling. Instead, she uses a marvelous technique: she focuses on the little things.
In the past I've encouraged readers to look through their old stories. It's encouraging to see both where we came from and how far we've come since then. But I also want to encourage a stroll through your blog's archives, for some very different reasons. 
