I have read many writing manuals over the years, some good, most terrible. But, honestly, you really don't need them. You learn how to write by reading books, and reading widely. I attended a writing workshop run by Christos Tsiolkas about 6-7 years ago and he pointed out to me that I was too narrow in my reading. I went out of my way to push myself out of my comfort zone and my writing saw a huge improvement as a result.
Recently I have been re-reading Tangled Webs by L.M.Montgomery. I loved it as a child so I thought I would sit down and work out why. Montgomery's descriptions in this books are out and out brilliant, and I have been jotting them down while I read so I can learn from them. She has a lot of characters that she needs you to remember really quickly, so she uses concise, vivid imagery. Here are some of my favourites:
"There was a grin of enjoyment on his little, wrinkled face with its curious resemblance to a shrivelled apple, and his astonishingly young, vivid blue eyes twinkled."
"Aunt Becky, her eyes as bright as a cat's, was ready to receive her guests."
"Margaret Penhallow, her thin, sensitive face flushing pitifully and her peculiarly large, soft, grey-blue eyes filling with tears, went blindly to the first vacant chair."
"with her patient, haggard face and her dark, hollow eyes in which still burned the fires of the hope that kept her alive"
"Big Sam had a face that was actually broader than it was long and a flaming red beard."
"nobody would ever dream of calling the fat, shabby, old fellow [a dandy] now, with his double chin, his unkempt hair and his flabby, pendulous cheeks."
I could honestly keep going with more examples.
So there you have it, reading with intent, being conscious of fiction you enjoy and analysing why are all vital to becoming a skilled writer.