William Zinsser's classic On Writing Well contains outstanding advice for writers, but the part I constantly think about is the section on editing:
Learn to enjoy this tidying process. I don't like to write; I like to have written. But I love to rewrite. I especially like to cut: to press the DELETE key and see an unecessary word or phrase vanish into the electricity. I like to replace a humdrum word with one that has more precision or color. I like to strengthen the transition between one sentence and another. I like to replace a drab sentence to give it more rhythm or a more graceful musical line. With every small refinement I feel that I'm coming nearer to where I would like to arrive, and when I finally get there I know it was the rewriting, not the writing, that won the game.