These are the ones that can ruin your credibility as a writer and a blogger.
1. Fewer vs. less
Unforgivable: There are less days in February than in March. Correct: There are fewer days in February than in March.
Use fewer when referring to things that can be counted — for example, “She ate fewer cupcakes tonight than she did last night.” Use less when referring to amounts that cannot be counted, or volumes: “The cupcakes had less frosting yesterday.”
2. Affect vs. effect
Unforgivable: Our services will have a positive affect on your business. Correct: Our services will have a positive effect on your business.
While affect and effect can be both be used as a noun and a verb, the rule of thumb for common usage is affect as a verb and effect as a noun. In the example above, the effect is the result of the services. In the sentence, “Our services can affect how customers see your business,” affect is to produce an effect upon, or to influence.
3. Pronoun/antecedent disagreement
Unforgivable: If you hire a professional copywriter, make sure they know how to write. Correct: If you hire a professional copywriter, make sure she knows how to write.
In the above sentences, copywriter is singular. So the pronoun should be singular, as well. Many people avoid gender-specific pronouns, but all too often, that just leads to bad grammar. The correct choices including using “he or she,” picking either he or she and sticking to that gender throughout the copy, or using a plural antecedent (which is the noun to which the pronoun refers): “When hiring copywriters, make sure they know how to write.”
Unforgivable: Are you on Goggle+? Correct: Are you on Google+?
Be sure to proofread your work. Misspelling the name of a company, a website or a person is a sign of sheer laziness.
5. It’s vs. its
Unforgivable: The pizza became famous for it’s unique flavors and toppings. Correct: The pizza became famous for its unique flavors and toppings.
This is a common mistake because technically, it’s follows the rule of using an apostrophe to convey possessives (for example, the pizza’s flavor). But an apostrophe is only used for the contraction of it is or it has: “It’s the best pizza ever!”
6. Misuse of the semicolon
Unforgivable: I love to write; but I hate using semicolons. Correct: I love to write; I hate using semicolons.
Semicolons can get confusing, so rather than make an unforgivable mistake, I tend to avoid them whenever possible. Use a semicolon to connect two related independent clauses without a conjunction, or within a complex series: “I’ve lived in Waukegan, Ill.; Alameda, Calif.; and Bartlett, Tenn.” Do not use a semicolon with a conjunction (and, but, for, or, so, nor, yet).
7. Alot vs. a lot
Unforgivable: Alot of people make this mistake. Correct: A lot of people make this mistake.
Alot is not a word!
Unforgivable: His favorite colors are red, blue and green. My favorite colors are yellow, purple, and pink. Correct: His favorite colors are red, blue and green. My favorite colors are yellow, purple and pink.
All four of the above sentences are actually right, but the top two are inconsistent because the second sentence uses the Oxford comma and the first does not. Don’t use the Oxford comma in one sentence and leave it out the next. Don’t spell out ten in the first paragraph and write 10 in the last. Writing rules change depending on what style of writing you follow (Chicago Manual or Associated Press), but whatever style you use, be consistent throughout your copy.
9. Poorly cited stats and quotes
Unforgivable: Women make up 97 percent of Pinterest users. Correct: According to AppData, women make up 97 percent of Pinterest users.
Back up statistics and quotes by letting your readers know where you got the information. If you can, provide a link back to the exact Web page where you found the data. Failure to prove where you got your facts will just make your content weaker.
10. Then vs. than
Unforgivable: I enjoy sitting much better then running. Correct: I enjoy sitting much better than running.
Than is used for comparisons, while then is used to refer to a point in time or “in addition to.” For example: “Back then, I was strong enough to run a marathon. Now, my body and health are different than they used to be.”
11. Lose vs. Loose
Unforgivable: If you loose your keys again, I’m not letting you in. Correct: If you lose your keys again, I’m not letting you in.
Lose is a verb, and loose is most commonly used as an adjective. Use loose when referring to something that doesn’t fit or isn’t secure, such as loose pants or loose attachments. Loose can also be used as a verb — for example, “loose a knot” — but in these cases, loosen is a more common word.
12. Stolen content
Unforgivable: Always. Correct: Never.
This one isn’t really a mistake, but rather just plain wrong. Never steal and use content that isn’t yours and play it off as your own work. Not only is that theft — it’s copyright infringement. Write original, informative content, and always proofread your work.