This pithy book is fun to read:

Wilson, Douglas. Wordsmithy: Hot Tips for the Writing Life. Moscow, ID: Canon, 2011. 120 pp.

Wilson gives seven pieces of advice (pp. 10–11):

1. Know something about the world, and by this I mean the world outside of books. This might require joining the Marines, or working on an oil rig or as a hashslinger at a truck stop in Kentucky. Know what things smell like out there. If everything you write smells like a library, then your prospective audience will be limited to those who like the smell of libraries.
2. Read. Read constantly. Read the kind of stuff you wish you could write. Read until your brain creaks. Tolkien said that his ideas sprang up from the leaf mold of his mind: your readings are the trees where your fallen leaves would come from. Mind mulch. Cognitive compost.
3. Read mechanical helps. By this I mean dictionaries, etymological histories, books of anecdotes, dictionaries of foreign phrases, books of quotations, books on how to write dialogue, and so on. The plot will usually fail to grip, so just read a page a day. If you think it makes you out to be too much of a word-dork, then don’t tell anybody about it. Let’s keep it between you and me.
4. Stretch before your routines. If you want to write Italian sonnets, try to write some short stories. If you want to write a few essays, write a novel, or maybe a novella if you are pressed for time. If you want to write haiku, then limber up with opinion pieces for The Washington Post.
5. Be at peace with being lousy for a while. Chesterton once said that anything worth doing was worth doing badly. He was right. Only an insufferable egoist expects to be brilliant first time out. Some writers—those who live charmed lives—have been brilliant first time out, but this happens so rarely that we shouldn’t care who they are. You can’t copy them anyway. You can copy those who got good.
6. Learn other languages, preferably languages that are upstream from ours. This would include Greek, Latin, and Anglo-Saxon. The brain is not a shoebox that “gets full,” but is rather a muscle that expands its capacity with increased use. The more you know, the more you can know. The more you can do with words, the more you can do. As it turns out.
7. Keep a commonplace book. Write down any notable phrases that occur to you or that you come across. If it is one that you have found in another writer, and it is striking, then quote it, as the fellow said, or modify it to make it yours. If Chandler said that a guy had a cleft chin you could hide a marble in, that should come in useful sometime. How could it not come in useful? If Wodehouse said somebody had an accent you could turn handsprings on, then he might have been talking about Jennifer Nettles of Sugarland. Tinker with stuff. Get your fingerprints on it.

The rest of the book breaks down each suggestion into seven more pieces (a chapter for each). Here are some excerpts:

1. There are some writers that I want to read no matter what they are talking about—because they are the kind of writers who write about things they love. (p. 26)
2. Reading solely within one genre is a form of literary provincialism, and it will provide you with a distinctive but unhelpfully narrow accent. (p. 31)
3. [R]ead like someone who will forget most of it. . . . Most of what is shaping you in the course of your reading you will not be able to remember. . . . Most of the good your reading and
   education has done for you is not something you can recall at all. . . . open. You read widely to be shaped, not so that you might be prepared to regurgitate. (pp. 34, 36)
4. [W]hen you have been to a number of other places, the content of your conversation is more interesting. Who would you rather listen to: someone who has been around the world three times on a oil freighter, or someone who never came out of his basement—even if he had really sweet bandwidth down there? (p. 66)
5. In the eighteenth century, during the ascendancy of the English dictionary makers and grammarians, it was foolishly thought that Latin was superior to English, and that things which couldn’t be done in Latin, like ending sentences with prepositions, shouldn’t be done in English. This is where we get the absurd rule that one must never, ever, end a sentence with a preposition. As Winston Churchill put it, “That’s the sort of nonsense up with which we shall not put.” . . . Another dumb thing was that it was thought that because Latin infinitives, being one word, could not be divided with an adverb, this meant English infinitives should not be so divided. . . . All this said, fussy grammarians need friends too, and so you may seek out and encourage them. Drop them a little note, telling them that they are your very favorite fussy grammarian, out with whom you like to hang. And if anybody winced there at my use of a plural pronoun for an indefinite singular, then may I suggest counseling? (pp. 99–100)

Related: Six Useful Books on Writing