Basic Book Design/Capitalizing Words in Titles
General Capitalization Rules 
These rules are adapted from The Chicago Manual of Style for clarity in the modern age of computers and the Internet.
1. The first and last words are always capitalized, even if fewer than five letters.
2. Words over five letters are always capitalized.
3. Verbs are always capitalized, even if fewer than five letters.
4. Nouns are always capitalized, even if fewer than five letters.
5. Unless the first or last words of a title, these are never capitalized: articles: a, an, the; conjunctions: and, but, or, not; prepositions that are fewer than five letters long: at, by, for, from, in, into, of, off, on, onto, out, over (unless used as a verb), up, with; infinitives: to; "as" is never capitalized; o'Clock (since it means "of the clock")
6. These words are capitalized, even though they are fewer than five letters. also, be, if, than, that, thus, when
7. Parenthesis and alternate titles: Some songs, and less commonly books and movies, will have parenthesis in their names. If the content of the parenthesis is an alternative song title then the above rules for capitalization apply. Consider the Simon & Garfunkel song "A Simple Desultory Philippic (or How I Was Robert McNamara'd into Submission)". The word "or" is not capitalized, even though it is the first word inside the parenthesis, because it is not part of the alternate title. The word "or" is not needed when the content of the parenthesis is clearly an alternate title. When the content of the parenthesis is also part of the title, the above six rules apply. An example is Buzzcocks' song "Ever Fallen in Love (with Someone You Shouldn’t Have)?"
The word "or" is not needed when the content of the parenthesis is clearly an alternate title.
In the movie Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb, which is sometimes referred to simply as Dr. Strangelove, there is a colon (:) after the "or". The colon is completely optional and may be included or excluded from the title by the author.
Exceptions: When prepositions are use as "phrasal verbs" they are capitalized to show that they are part of the verb, and not showing physical relations between nouns. Examples are Turn On or Turn Off or Give Up. Note that the word "up" is more often used as part of a verb than as a physical preposition. Likewise, a song called "Blow Up" would have a similar meaning to exploding, and not blowing in an upwards direction.
Related rules 
The names of books, movies, and music albums are italicized.
The names of songs are in "quotation marks".
Links and hyperlinks for the Internet are underlined.
There is some debate between authors of style manuals of some of these rules, mostly on italicizing versus underlining. When writing with a pen and paper, it is extremely difficult to clearly italicize text so the reader knows the author is referring to titles. Thus, writers will normally underline words instead of italicize them. With the invention of computers and text editors, italicizing and underlining has become simple. However, with the popularity of the Internet, underlining has become reserved for links.
The purpose of italicizing or underlining is to clearly show the reader of text that certain words belong to titles. If a writer is writing with pen and paper they may choose to underline instead of italicize. The most important issue is to not switch between styles; all titles of books, movies, and albums should be either italicized or underlined.