Some word pairs in English are so close in look and sound that a lot of journalists, even good ones, mix them up. This is the working reference Simon used to check himself. Read it, remember the rules, and when you are stuck, come back to the example.
Affect vs effect
Affect is a verb. It means to influence. "The policy affects teachers." Effect is a noun. It means the result. "The policy had an effect on teachers." There are exceptions (effect can be a verb meaning to bring about: "to effect change"). Ignore them for now. Use affect as a verb, effect as a noun, and you will be right ninety-nine times out of a hundred.
Compliment vs complement
A compliment is praise. "She gave him a compliment about his hat." A complement completes or matches. "The wine complemented the dinner." Both words can be nouns or verbs, but they mean different things. If you mean praise, the "i" word. If you mean matches, the "e" word.
Alternate vs alternative
In Australian English, alternate means "every other one" (alternate days). Alternative means "another option" (an alternative route). American usage blurs this. Australian usage does not. Simon was particular: "If there is only one choice, it is not an alternative. It is the choice."
There vs their vs they're
There: a place. "The notebook is over there." Their: possessive. "It is their notebook." They're: contraction of "they are." "They're coming." If a journalist writes "their" when they mean "there" in a published piece, the journalist should reread every piece they filed that month.
Die vs pass away
People die. Journalists write that they died. "Pass away" is a euphemism borrowed from American funeral directors. It is not clearer or kinder. It is a circumlocution. Use it only if the family has asked you to and the sensitivity outweighs the directness.
Every day vs everyday
Every day: each day. "I read the paper every day." Everyday: ordinary, routine. "My everyday shoes." If you can substitute "each day" and the sentence still works, use two words. Otherwise one.
Actually (mostly delete it)
Ninety-five percent of the time, the word actually in your copy is filler. "I actually disagree" means "I disagree." "He actually said" means "He said." Delete it. Read the sentence again. It is tighter and stronger. The only defensible use is when you are contrasting with something known: "The report said the budget was on track. Actually, it was $40 million over." There, it earns its place.
Don't start a sentence with "I" (Simon's rule)
Simon's rule was that no feature intro should start with the word "I." A journalist starting with "I" is pointing at themselves instead of the story. If you genuinely need to be in the first sentence because you are part of the story, start with the action and put "I" later: "Walking into the building, I noticed..." rather than "I walked into the building and noticed..." The rule is about the reader's first impression, not about first-person writing in general.
Other pairs to watch
Principal / principle. Principal is the head of a school or a main thing. Principle is a rule or ethic.
Stationary / stationery. Stationary is not moving. Stationery is paper and pens.
Discrete / discreet. Discrete is separate. Discreet is careful.
Peak / peek / pique. Peak is a top. Peek is a glimpse. Pique is to annoy or stir curiosity.
Past / passed. Past is a time. Passed is the past tense of pass.
Lose / loose. Lose is to misplace or fail to win. Loose is not tight.
Its / it's. Its is possessive. It's is the contraction of it is.
A general rule
If you are not sure, check. The dictionary takes thirty seconds. Getting it wrong in print takes a lifetime to shake off. Simon used to say that a journalist's reputation is mostly built on never being the person whose copy has to be corrected in print.