Any sufficiently advanced technology is indistinguishable from magic.

Sturgeon's Law (as in Theodore Sturgeon):

Ninety percent of anything is drek.

1--write

2--finish what you write

3--revise only at the request of an editor

4--send it out

What Harry Turtledove said was that Heinlein did not mean writers should not polish and rewrite their stories. They should do that--first drafts are rarely ever of publishable quality.

Turtledove said that Heinlein was saying if a writer comes up with an idea that could be added to the story, the writer should save it for a new story--only add ideas when an editor (someone who is going to pay you money) asks you to.

Now, my comments:

There are two aspects of writing that every writer should consider: story-telling and word-smithing (also known as story and discourse, or content and expression).

Putting ideas together, working out characterization, story structure, plot, setting, etc, etc, etc, are all part of story-telling (figuring out what the story is that you are telling).

If you do your story-telling first, you have a better chance of obeying Heinlein's law #2.

Once you've got a first draft completed, then you can worry about word-smithing (description, word choices, style, voice, and so on--how you tell the story you are telling).

There are probably billions of brilliant first sentences out there, and millions of dazzling first paragraphs, and hundreds of thousands of exquisite first pages, and tens of thousands of wonderful first chapters, but few people will ever see them because the authors stopped working on the story-telling and concentrated on word-smithing one sentence or one paragraph or one page at a time and never managed to finish the story.

Heinlein, if Turtledove is right, was saying get the story written down (do the story-telling) and then do the word-smithing, and don't go back to story-telling once you've got a good story (don't change the ideas, the structure, the characters, or whatever).

1. Read a lot.

2. Write a lot.