I have lots of great ideas for novels. Just can't write fiction worth beans. About 10 years ago I was hot to write a novel about what google is attempting to do by putting all published text online and indexed. I thought it was a pretty good idea.
You too, huh? I kinda wish there were some job openings for muses out there...
How many words of fiction have you written?
Write 200,000-300,000 words and see what you think of your writing style then.
How, you ask?
You sit down and you write; Steinbeck has a good treatise on writing (Journal of a Novel); read and emulate that.
The real key is to write every day, five (or however many) days a week. Every week. Rack up lots of words. Don't go to writing seminars, just write!
When you are done you edit. Editing is easy. You just have to throw away about half of what you wrote (ignore the blood your are losing).
When you are done, you get to the hard part: selling the sucker.
But first, you have to crank out the words. Don't worry at first how good they are, just get them down. Don't go back and edit until you are done. WRITE! And then WRITE SOME MORE!
[The rest is left as an exercise for the student...]