With the advent of texting, and the fact you have to hit a few extra buttons to make something upper case (otherwise known as a capital letter), people have been forgetting the basics of capitalization.
Here's a few quick rules:
1) The first word of a complete sentence is capitalized. Depending on the style book, sentences following colons and quoted sentences may also be capitalized.
2) The pronoun "I" is always capital. (You'd be surprised how often I see this mistake in my students' papers.)
3) Professional titles are capitalized when used to address someone: Mr., Doctor, Senator.
4) Proper Nouns are capitalized: Katie, New Zealand, Arkansas, French.
5) Titles of books, movies, televisions are capitalized, except for minor words: Roots, Lord of the Ring, Hairspray.
1) The seasons (fall, winter, spring, summer) are not capitalized.
2) School subjects, except for languages (English, French, Spanish), are not capitalized, unless used as the title of the course. Then they would be considered a proper noun and would be capitalized. Examples include math, physics, and band.
3) Only the titles of specific government positions and groups are capitalized, because they are proper nouns. Generalities, like senators, lobbyists, or a bureau, are not capitalized, while titles like the FBI, Congress, and the President are.
Keep this in mind the next time you're proofreading. Capitalized is fairly easy to get a grasp on, but if you don't think about it, stupid mistakes can easily make your manuscript look very sloppy, very quickly.