Happy are they who don't doubt themselves and whose pens fly across the page. I myself hesitate, I falter, I become angry and fearful, my drive diminishes as my taste improves, and I brood more over an ill-suited word than I rejoice over a well-proportioned paragraph.
What is above all needed is to let the meaning choose the word, and not the other way around. In prose, the worst thing one can do with words is surrender to them. When you think of a concrete object, you think wordlessly, and then, if you want to describe the thing you have been visualizing you probably hunt about until you find the exact words that seem to fit it. When you think of something abstract you are more inclined to use words from the start, and unless you make a conscious effort to prevent it, the existing dialect will come rushing in and do the job for you, at the expense of blurring or even changing your meaning. Probably it is better to put off using words as long as possible and get one's meaning as clear as one can through pictures and sensations. Afterward one can choose—not simply accept—the phrases that will best cover the meaning, and then switch round and decide what impressions one's words are likely to make on another person. This last effort of the mind cuts out all stale or mixed images, all prefabricated phrases, needless repetitions, and humbug and vagueness generally.