When you know you're going to go over your work and cross out everything that doesn't work you can just start writing - and keep writing even if it's rubbish it doesn't matter because you can cross it out later. Well, of course. That's a boring bit of writing - because it's too fast. Slowing stories down also gives you time to get to know the characters in the story. I'm not going to start snivelling if the dragon crunches up their bones.
Long stories are usually more effective than short stories.
Always make your stories as long as you can. Most of the time you won't be able to make them very long - you won't have time. But if you can write a little bit of a long book instead of trying to cram all the ideas in your head into a few pages - because that way you won't get into the habit of writing books that gallop. Make it fat. Now you've got a fat story.