Here are some general rules about what should be capitalized.
The first word in a sentence.
The pronoun "I"
A title used with a last name
Opening of a letter (salutation)
Closing of a letter
Titles of books, stories, essays
Proper nouns
First word in a quote
Languages, races, nationalities
Historical events and documents
The dog is angry. How are you?
She and I are happy.
President Obama, Count Olaf, Queen Elizabeth
Dear John,
Your friend, Best wishes, Sincerely,
Because of Winn-Dixie, Bridge to Terabithia
Jason Hammack, Wal-Mart, Bland Elementary
She said, "How are you?"
English, Chinese, German, French, Jewish
Battle of the Alamo, Declaration of Independence