I've been writing for years and find the best way is to just go for it. Don't be too judgemental of what you write. You end up doing several drafts and edits anyway once it's done. But you can't perfect what's not there so you've got to get it going first. You'll probably find once you start that the story evolves as you go on and you get more feelings for your characters and plot. I generally try to do some writing everyday even if it's only for a short time. Whenever I've finished something I go over it and probably end up with two or three edits before showing anyone else.