Most of us know (or should know) that the first word of a sentence and the pronoun I are always capitalized.
There are other ways capital letters are used (and often misused). What follows is a short capitalization guideline.
The first word of a sentence
The pronoun "I"
Example: The first time I went to New York I was overwhelmed.
Proper nouns (the names of specific people, places, organizations, and sometimes things)
Example: The United Nations, Golden Gate Bridge, Vancouver, Winston Churchill
Family relationships (when used as proper names)
Example: I sent a get well soon card to Aunt Tina.
The names of God, specific deities, religious figures and holy books
Example: the Qur'an, Zeus, Buddha
There is an exception to this. Do not capitalize the non-specific use of the word "god."
Example: The word "polytheistic" means the worship of more than one god.
Title preceding names,
Example: He is the assistant to Mayor Blumenthal
but not titles that follow names
Example: I interview Candice Bee, mayor of Lakeville
Directions that are names (North, South, East and West as sections of a country but not as compass directions)
Example: The Lees live in the Northeast.
The days of the week, months of the year and holidays
Example: Thanksgiving, March, Saturday
The seasons when used in a title
Example: The Summer 2009 semester
The names of countries, nationalities and specific languages
The first word in a sentence that is a direct quote
Example: Shakespeare once wrote, "To be or not to be..."
Members of national, political, racial, social, civic and athletic groups
Periods and events
Exmaple: Elizabethan Era
Trademarks
The abbreviations of specific names
Example: RBC (Royal Bank of Canada), UN (United Nations)