According to most style guides, nouns, 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 word). The example below illustrates this rule:
The and in Romeo and Juliet should not be capitalized because it is a conjunction. 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.