For writing, here’s the approach I’ve found works best for me, by far:

• Clearly note the purpose & main points (1 to 5)
• Write the first draft as quickly as possible
• [Maybe] do a light editing pass
• Set aside for an hour/day/week
• Return, edit into shape, publish

Editing is where the real work happens, and I find it easier (and more enjoyable) than writing the first draft.  I’m a rabid fan of the Strunk and White School of Editing.