Teach your students to eliminate unnecessary words. Show them examples from Strunk's catalog of needlessly wordy phrases in common use.
"The question as to whether" becomes "Whether (the question whether)."
"There is no doubt but that" becomes "No doubt (doubtless)."
"He is a man who" becomes "He."
"His story is a strange one" becomes "His story is strange."
Explain why the active voice is usually preferable to the passive voice. Highlight the difference between the following two sentences, which Strunk uses to illustrate the strength of the active voice:
"I shall always remember my first visit to Boston."
"My first visit to Boston will always be remembered by me."
The second sentence is longer and less forceful. It is also unclear: who will always remember the writer's first visit to Boston --- the writer himself or another party?
Make them see how a plain but forceful style often succeeds over a highfalutin' one. George Orwell gives the following humorous example, from his classic essay "Politics and the English Language," of a passage from the Book of Ecclesiastes in the King James Bible translated into stilted "Modern English":
Original
"I returned and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favour to men of skill; but time and chance happeneth to them all."
Modern
"Objective considerations of contemporary phenomena compel the conclusion that success or failure in competitive activities exhibits no tendency to be commensurate with innate capacity, but that a considerable element of the unpredictable must invariably be taken into account."
Draw attention to the extra length, the unnecessary use of technical and scientific terms and the vague, abstract tone in the second sentence.