Don't walk on your sprained ankle or it will take longer to heal.

ankle, or

Comma before joining word between independent clauses. (both parts are complete sentences)

The Grand Canyon is not far from Flagstaff Arizona.

Flagstaff, Arizona

Conventional Situation. City, State

You old torn pants indicate that this is not a formal visit.

old, torn

Comma separating adjectives describing the same noun. (old and torn describe pants)

Before paper was invented maps were made of whatever materials were at hand.

invented, maps

Comma after introductory element

(prepositional phrase, before=preposition)

The villagers fled from the erupting lava suffocating ash and deadly fumes of the volcano.

lava, suffocating ash, and deadly

Comma before coordinating conjunction when items are in a series

(list 3 or more things).

The spy in the movie to give you a hint is someone you'd never suspect.

movie, to give you a hint, is someone

Commas surrounding a sentence interrupter.

(gives more information about movie)

Is this product advertised as one of those new improved soaps?

new, improved

Comma to separate adjectives that go with the same noun.

(new and improved describe the soap)

She told me her birthday was February 11 1978.

11, 1978

Conventional Situation. Day, year.

Have you ever experienced such a miserably cold wet summer?

cold, wet

Comma separating adjectives describing the same noun. (cold and wet describe summer)

Mrs. Peabody who loved the movies always brought her own popcorn.

Peabody, who loved the movies, always

Commas to set off a sentence interrupter.

(gives more info about Mrs. Peabody) 

If I had known it was going to be such hard work I might not have taken the junior course in creative writing.

work, I

Comma after introductory element.

After discarding polo and ice hockey for the same reason I found inspiration.

reason, I

Comma after introductory element.

(prepositional phrase, after=preposition)

It is the pressure of getting work in on time not the work itself that gets on my nerves.

time, not the work itself, that

Commas to set off a sentence interrupter. 

The reunion was held on Wednesday June 16 1998.

Wednesday, June 16, 1988

Conventional Situation. Dates

Will you spend your vacation in the mountains on the lake or at the seashore?

mountains, on the lake, or at the seashore

Comma before coordinating conjunction when there are items in a series.

(list 3 or more things)

The coach expects discipline hard work and quick thinking from every person on the team.

discipline, hard work, and quick thinking

Comma before coordinating conjunctions when there are items in a series.

(list 3 or more things)

This was out last watch fire and there were reasons why I should remember it better than any of the others.

fire, and there

Comma before joining word between independent clauses. (both parts are complete sentences)

There was Tip Smith destined by his freckles and red hair to be the buffoon in all of our games.

Smith, destined by his freckles and red hair, to be

Commas to set off a sentence interrupter.

(freckles and red hair gives more info about Tip Smith)

The policeman tried but Herbie threw his gears into reverse and pushed back.

tried, but

Comma before joining word between independent clauses. (both parts are complete sentences)

Tom the oldest by a few minutes was first in the rush for their little cat door.

Tom, the oldest by a few minutes, was

Commas to set off sentence interrupters.

(oldest by a few mins. gives extra info about Tom)

The permeable porous cell membrane is composed of mainly lipids.

permeable, porous

Commas separate adjective describing the same noun.

(permeable and porous describe the cell)

The Jarada an exacting and reclusive race have contacted the Federation with a request to negotiate an exchange of ambassadors.

Jarada, an exacting and reclusive race, have

Commas to set off a sentence interrupter. 

I got the horse moving by shortening the reins leaning my body slightly forward and squeezing with both my legs.

reins, leaning my body slightly forwards, and 

Comma before coordinating conjunctions when there are items in a series. 

"The Practice" is poised to become a bona fide hit and it features the best cast on television.

hit, and

Comma before joining word between independent clauses.

Tiffany's soft cascading curls go with her princess-style dress perfectly.

soft, cascading

Commas separate adjectives describing the same noun.

(soft and cascading describe the curls)

A friend loves at all times and a brother is born for adversity.

times, and

Comma before joining word between independent clauses.

(both parts are complete sentences)

Many intelligent well-educated scientists are convinced we will pick up signals from another planet.

intelligent, well-educated

Commas separate adjectives describing the same noun.

(intelligent and well-educated describe the scientists)

Despite a pair of sacks and two interceptions Leaf led the Bills to win 19-16.

interceptions, Leaf

Comma after introductory elements.

Friendships go through all kinds of stages and this is a test of yours.

stages, and

Comma before joining word between independent clauses.

(both parts are a complete sentence)

If I get close to them and they have fun they're liable to do what other young actors do.

fun, they're

Comma after introductory elements

Feudalism was a caste system a property system a military system and a system of social behavior.

caste system, a property system, a military system, and a system

Comma before coordinating conjunction when there are items in a series

(list of 3 or more items)