I didn't really talk much about capitalization yet so here we go:

Things that should be capitalized include:
-The first word of every sentence
-Proper nouns (names, places, companies, etc.)
-Every letter of an abbreviation
-The first letter of titles used for addressing (Doctor, Mister, etc.)

Things that should not be capitalized include:
-Basically every other word
-Common nouns (desk, computer, pencil, street, etc.)
-Pronouns

There are two exceptions I am aware of pertaining to that last rule, and those are:
-I. I should always be capitalized
-If you are referring to God, especially in a religious context, by a pronoun, He should be capitalized

So... yeah!