First… Get it down! Start with something, anything! You can always edit it later. If you're stuck, imagine you're talking about your subject to a friend and write it down, or install a speech recognition program and talk to that.
On style… I find I write the introduction last when I'm
explaining something, and first when I'm writing about people. Go
figure. Pick the style or styles that work for you. Some writers I
know outline, some just "let it spew."
On revising…Shelf time really helps. Read everything you've
written until you can't stand it any more, then give it a day or even
ten minutes of shelf time and read it again. Read out loud and you'll
hear your mistakes. Speaking of mistakes, try not to solicit feedback
on anything you've written until you've done your absolute best and
used up your own personal bag of tricks. Keep your spell checker in
that bag of tricks as your best friend. I really think that typos
reproduce on the page while we're sleeping.
On criticism…Ask people for specific comments… Say, for example, "Did it flow easily?" instead of "Did you like it?" Another great way to find out what someone thinks is to watch them read your piece to see their facial expressions…when they laugh, when they cry, when they look like they have no idea of what you're saying. Of course, being thick skinned is the tricky part. This can help: Try taking the focus off of you and put it onto your writing and your goal to make your writing sparkle.
On deadlines…I usually like deadlines, because they help me focus and plan, and curb my human tendency to procrastinate.
Making it look good…The unfortunate reality is that people do judge a book by its cover. Make whatever you've written look good by writing neatly or typing, adding headings and page numbers, and spell checking each revision. A neat, attractive page gives your message stature and draws readers.
Vividness..The best creative writing is the most vivid. When you can see what the curly-haired writer is talking about in your mind's eye, or can feel what she's feeling, it's vivid-- it's the writer-reader mind meld we all shoot for. One cheap trick (that works) is to liberally use colors, smells, textures, sounds, and tastes to describe anything, including that toasted brown salty pretzel you crunched into last night.