According to most style guides, nouns, pronouns, verbs, adjectives, and adverbs are the only words capitalized in titles of books, articles, and songs. Prepositions, articles, and conjunctions aren’t capitalized (unless they’re the first or last word). The example below illustrates this rule:
The and in Romeo and Juliet should not be capitalized because it is a conjunction. The exception to the rule, when it comes to prepositions, is that if the word contains six or more letters, it should be capitalized.
Consider these additional examples of correctly capitalized titles:
The same rule regarding title capitalization applies to subtitles. See the examples below:
In this particular example, the article “a” is capitalized because it is the first word of the subtitle.