“Shoe-in” vs. “Shoo-in.”
This expression purportedly comes from the practice of corrupt jockeys holding their horses back and shooing a preselected winner across the finish line to guarantee that it will win. A “shoo-in” is now an easy winner, with no connotation of dishonesty. “Shoe-in” is a common misspelling.
Or this one: “If I was” vs. “If I were.”
The subjunctive mood, always weak in English, has been dwindling away for centuries until it has almost vanished. According to traditional thought, statements about the conditional future such as “If I were a carpenter . . .” require the subjunctive “were,” but “was” is certainly much more common. Still, if you want to impress those in the know with your usage, use “were” when writing of something hypothetical, unlikely, or contrary to fact.
The same goes for other pronouns: “you,” “she,” “he,” and “it.” In the case of the plural pronouns “we” and “they” the form “was” is definitely nonstandard, of course, because it is a singular form.
I’ve found this website of common English usage errors to be most helpful in my writing, especially during my academic studies. You’ll be amazed at how many errors you make. The book would be a great gift for students of all ages.