Every pronoun should agree with its antecedent.

Words such as it, she, he, and they are pronouns. A pronoun takes the place of a noun. That noun is known as the pronoun's antecedent. Both the antecedent and the pronoun must agree. A singular noun cannot be replaced by a plural pronoun.

Watch out for sentence fragments.

It is a rule of grammar that every sentence must have a subject and a verb. “Sentence fragments” in the first example has neither a subject nor a verb.

The instructor advised her class to avoid passive voice.

In the first sentence, there is no actor. There is nothing to tell us WHO is giving the advice. Instructors hate this. Always be clear about WHO is DOING what.

Proofread every sentence for misspellings and typos.

Writing is the culmination of your thinking. It represents you when you are not there to represent yourself. You should therefore always proofread as well as spell-check.

It's essential to use apostrophes correctly.

There are two basic rules to using apostrophes. An apostrophe can indicate that letters are missing -- as with the first “it's” which is a contracted form of it is. It can also signify possession. If we wrote “The dog's ball bounced across the grass,” for example, the apostrophe would tell you that the ball belongs to the dog.

Ordinarily, you shouldn't use abbreviations.

If you think something is worth writing down, it's worth writing down in full. Abbreviations suggest that you didn't want to invest the time and effort it takes to write out a complete word.

As a rule, never end a sentence with a preposition.

Prepositions are words such as above, before, between, during, from, in, into, of, since, through, to, until, and with. A preposition joins words or phrases together. In the first example above, “with” does not lead to a concluding word or phrase. In the second example, “with” connects “sentence” to “preposition.” “With” connects rather than concludes.

Do not dangle participles in your writing.

Do not speak like Yoda. In the first example of this sentence, the participle is the word “dangled.” A participle acts as an adjective describing a noun or pronoun. We edited the sentence to make it clearer in example two, and removed the participle altogether. A good rule of thumb for spotting dangling participles is to ask yourself “do I sound like Yoda?” If you do, something needs to change.

People like you and me should have no problems with grammatical case.

“I” always refers to the subject of a sentence. “Me” always refers to the object of a sentence. A quick way to check if you have this correct is to remove the “you” and see if the sentence makes sense. “People like I,” for example, is nonsense. “People like me,” however, is grammatically correct.

Take care never to split infinitives.

An infinitive is the word “to” followed by a verb. In these sentences, the infinitive is “to split,” words that have been separated in the first example by the word “never.” “To” and its accompanying verb should always be together.

In letters, themes, and reports, use commas to separate items in a list.

If you make a list of any type in your paper, you should use commas to separate each word from the next.

Don't be someone who confuses who and whom.

We've done two things in this sentence. The first is that we've simplified it to make the point more clear. The second is we replaced the first “whom” with “who.” Who refers to subjects, whom to objects.

A non-sequitur occurs when your thoughts do not connect. In the above sentence, studying harder has nothing to do with whether you write non-sequiturs. The two clauses are completely unrelated.

Verbs in any essay have to agree with their subject.

The subject of this sentence is plural – “verbs.” In this sentence, the word verbs is actually a noun. It must agree with its verb, which in this case is the word “have.”

If teachers have ever told you that you don't put a comma before "that," they were right.

A comma should separate clauses. In the above sentence, the first comma separates words that relate to the same subject. The comma should not keep them apart. The second comma, however, connects two separate clauses.