You Have to Work Every Day

It doesn't matter what time of day you work, but you have to work every day because creation, like life, is always slipping away from you. You must write every day, but there's no time limit on how long you have to write.
One day you might read over what you've done and think about it. You pick up the pencil or turn on the computer, but no new words come. That's fine. Sometimes you can't go further. Correct a misspelling, reread a perplexing paragraph, and then let it go. You have re-entered the dream of the work, and that's enough to keep the story alive for another 24 hours.
The next day you might write for hours; there's no way to tell. The goal is not a number of words or hours spent writing. All you need to do is to keep your heart and mind open to the work.
WALTER MOSLEY

Read your work aloud

Read your work aloud! This is the best advice I can give. When you read aloud you find out how much can be cut, how much is unnecessary. You hear how the story flows. And nothing teaches you as much about writing dialogue as listening to it.
JUDY BLUME

Omit needless words

Omit needless words. Vigorous writing is concise. A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts. This requires not that the writer make all his sentences short, or that he avoid all detail and treat his subjects only in outline, but that every word tell.
WILLIAM STRUNK, JR. and E.B. WHITE

Freewriting

Freewriting is the easiest way to get words on paper and the best all-around practice in writing that I know. To do a freewriting exercise, simply force yourself to write without stopping for ten minutes. Sometimes you will produce good writing, but that's not the goal. Sometimes you will produce garbage, but that's not the goal either. You may stay on one topic, you may flip repeatedly from one to another: it doesn't matter. Sometimes you will produce a good record of your stream of consciousness, but often you can't keep up. Speed is not the goal, though sometimes the process revs you up. If you can't think of anything to write, write about how that feels or repeat over and over "I have nothing to write" or "Nonsense" or "No." If you get stuck in the middle of a sentence or thought, just repeat the last word or phrase till something comes along. The only point is to keep writing. Or rather, that's the first point. For there are lots of goals of freewriting, but they are best served if, while you are doing it, you accept this single, simple, mechanical goal of simply not stopping. When you produce an exciting piece of writing, it doesn't mean you did it better than the time before when you wrote one sentence over and over for ten minutes. Both times you freewrote perfectly. The goal of freewriting is in the process, not the product.
PETER ELBOW