Always capitalize the first and last words of the title, regardless of what parts of speech they are. Also capitalize nouns, pronouns, adjectives, adverbs and verbs. An optional rule is to capitalize conjunctions or prepositions with five or more letters. The older, although still applicable, rule is to never capitalize any conjunction or preposition. Also capitalize subordinate conjunctions, such as "as," "although" or "because."
Don't capitalize articles: "a," "an" or "the." However, if an article is the first word in a title, it should be capitalized. Avoid capitalizing prepositions or conjunctions that are four letters or fewer, unless the preposition is the first or last word in the title. For example, do not capitalize "and," "nor" or "or." Don't capitalize "to" if it is used with an infinitive, unless it is the first or last word in the title as well.
Do not lowercase words that may work as other parts of speech just because they can function as prepositions. For example, "in" can be a preposition or an adverb, as in "bringing in." If the title has a phrasal verb like "setting up," capitalize "up," which functions as a particle instead of a preposition.
Do not put in lowercase all two-letter words just because they have two letters and resemble short prepositions like "up" or "of," which should be lowercase. If it is a noun, adjective, adverb or pronoun, capitalize it. Words like "is" and "it" often fall into this category.