A Capital Idea! - The Uses and Rules of Capital Letters

Capitalize the first word of every sentence — unless that sentence is in parentheses incorporated within another sentence.
Example: Glacial till or debris (some geologists call this material “garbage”) is often deposited in formations called morains.

Capitalize the personal pronoun I.

Capitalize the names of family relations when they are used as substitutes for names.
Example: Grandma and Grandpa live with Dad and Mom now.
but...
I went with my mom and dad to visit my aunt and uncle.
*Notice the role of the modifying pronoun here.

In titles, capitalize the first, last, and all important words. Usually, we don’t capitalize articles, prepositions, and coordinating conjunctions.
Example:War and Peace

Capitalize names of specific persons, places, and geographical locations.
Example: My brother Charlie, who used to live in the Middle East and write books about the Old West, now lives in Hartford, Connecticut.
but...
Don't capitalize directions.
Example: They moved up north, to the southern shore of Lake Erie.

Capitalize names of days of the week, months, and holidays.
Example: Valentines Day, which is always on February 14, falls on Tuesday this year.
but...
Don't capitalize the names of seasons
Example: Next fall, before the winter storms begin, we’re heading south.

Capitalize the names of historical events.
Example: The Battle of the Bulge was an important event in World War II.

Capitalize the names of religions and religious terms.
Example: God, Christ, Allah, Buddha, Christianity, Christians, Judaism, Jews, Islam, Muslims.

Capitalize the names of nations, nationalities, languages, and words based on such words.
Example: Somalia, Swedish, English muffin, Irish stew, Japanese maple, Jew’s harp, French horn

Capitalize the names of academic courses when they’re used as titles.
Example: He took Carpentry 101, but he did much better in his economics and English literature courses.

Capitalize brand names.
Example: Ford and Kleenex

Capitalize titles when they precede names.
Example: Dean Arrington introduced President Carter to Secretary Bogglesworth.
but...
usually not after a name
Example: Joe Chuckles, who was chairman of the board of directors in 1995, has since retired.

The best advice on capitalization: Consult a dictionary!