Some of the most common grammar mistakes are the easiest to avoid. Whether speaking or writing, correct grammar and spelling are important to your credibility and the impression you leave upon others.

Here are a few of the most common grammar mistakes with examples as to the correct usage.

Subject/Verb Disagreement:
When speaking or writing in the present tense, both subjects and verbs must be either singular or plural. A combination of singular and plural is incorrect.

Incorrect: The directions is confusing.
Correct: The directions are confusing.
Incorrect: One of these flowers bloom in the spring.
Correct: One of these flowers blooms in the spring.

Past Tense Errors:
Past tense regular verbs end with the suffix "ed" such as laughed and walked. Past tense irregular verbs change form completely. Be careful not to leave out the "ed" ending when using a regular past tense verb.

Incorrect: During the movie, she talk a lot.
Correct: During the movie, she talked a lot.
Incorrect: The water is freezed.
Correct: The water has frozen.

Sentence Fragments:
A sentence fragment lacks a verb, subject, or both and cannot stand alone as a sentence.

Incorrect: The performers who visited our school.
Correct: The performers who visited our school were amazing. Incorrect: Playing all day long.
Correct: We played all day long.

Apostrophe Errors:
An apostrophe is used to show possession. You should add an 's after a plural or single nouns that does not end in s. After a plural noun ending in s, you would only use an apostrophe alone.

Incorrect: Your parent's car is parked in the driveway. (2 parents)
Correct: Your parents' car is parked in the driveway.

Comma Errors:
Be cautious of missing commas in a series of items, missing commas after dependant introductory clauses, and missing commas in nonrestrictive clauses.

Incorrect: Sea animals fascinate him so he wants to be a marine biologist.
Correct: Sea animals fascinate him, so he wants to be a marine biologist.
Incorrect: Because she is ill she will not attend school today.
Correct: Because she is ill, she will not attend school today.
Incorrect: My car is small so it gets good gas mileage.
Correct: My car is small, so it gets good gas mileage.

Errors In Verb Tense Shift:
A verb tense shift happens when the speaker or writer switches from past to present or present to past without reason.

Incorrect: We drove to the pool, and the dog dives right in.
Correct: We drive to the pool, and the dog dives right in
Also correct: We drove to the pool, and the dog dove right in.

(WOL editorial note: In USA English 'dove' is commonly used for the past tense of dive. In UK English the past tense of dive is 'dived'.)