If, on re-reading your article, you are not quite sure what you meant when you wrote any passage, take it out altogether. Do not leave it in to puzzle the reader, even though you add a footnote—as Ruskin did—explaining that you have no idea what you meant when you wrote it.
In order to avoid an ambiguous style, two things are necessary: the ability to think clearly and concisely, and the ability to write down exactly what one thinks.
The Subject Should Regulate the Choice of Words
The choice of words should be influenced by the subject of your writing. A dignified subject calls for dignified language. A racy subject calls for racy language; and so on.
If your theme be a lofty one, do not "let down" the train of lofty thought it should engender, by introducing some word or phrase that induces a much lower—or a different—plane of thought and ideas. It is a backward policy, to say the least of it, to weaken, or obliterate, by ill-chosen language, the ideas you set out to foster in the reader. It is no extenuation to plead that the jarring phrase is particularly expressive; if it actually counteracts the ideas you seek to convey, it cannot be expressing your meaning.
The beginner often gets himself tied up in a knot with negatives; and even if he steer clear of actual error, he is apt to overdo himself with double negatives. It is better to make a direct statement in the affirmative if possible, than to involve it in negatives.
Instead of saying "a not uncommon fault," it is clearer at first sight if you say "a common fault," or "a fairly common fault." I know it does not always follow that the exact reverse fulfils the purpose of the double negative; a fault may be "not uncommon" and yet not exactly common. Nevertheless it is always possible to get the precise shade of meaning in the affirmative; and until a writer is quite fluent, it is better not to risk confusing the reader's mind by the introduction of too many negatives.
The Tendency to Use Involved Sentences
In the praiseworthy desire to use fine English, the beginner is very apt to get a sentence such a mixed-up maze of words that there seems little hope of the meaning ever getting out alive at the other end!
I take this from a MS. just to hand:—