One of my favourite sources of retweet material is Darcy Pattison's blog, Fiction Notes. If she was on Twitter (as far as I can tell, she's not), I'm sure she'd be one of the most retweeted writers ever.
(Edit: I've switch the link for this book to Amazon at Darcy's request since she says that indie bookstores may find it hard to obtain.)
Hm, and I notice she has a book on revision: NOVEL METAMORPHOSIS: UNCOMMON WAYS TO REVISE. Anyway, do visit her site for excellent tips on the craft of writing: