17. 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 makes all sentences short, or avoid all detail and treat subjects only in outline, but that every word tell. Many expressions in common use violate this principle.

the question as to whether -> whether (the question whether)
there is no doubt but that -> no doubt (doubtless)
he is a man who -> he
in a hasty manner -> hastily
her story is a strange one -> her story is strange
the reason why is that -> because

Imagine you're at a play. It's the middle of the first act; you're getting really involved in the drama they're acting out. Suddenly the playwright runs out on the stage and yells, "Do you see what's happening here? Do you see how her coldness is behind his infidelity? Have you noticed the way his womanizing has undermined her confidence? Do you get it?
You get it, of course, and you feel patronizd. You're an intelligent theatergoer, and what's happening on the stage is clear enough. You don't need the writer to explain it to you. This is exactly what happens when you explain your dialogue to readers. Consider the following:

"You can't be serious," she said in astonishment.

If you're like most beginning novelists or short-story writers, you write sentences like these almost without thinking. What could be easier than simply to tell your readers how a character feels? If she is astonished, you say so. It saves all sorts of time and trouble.
It's also lazy writing. When your dialogue is well-written, describing your characters' emotions to your readers is just as patronizing as a playwright running onto the stage and explaining things to the audience. "You can't be serious," conveys astonishment - no explanation is needed.
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Remember R.U.E: Resist the Urge to Explain.