Karen Reddick, The Editor’s Blog

Always capitalize the first and last words both in titles and in subtitles and all other major words (nouns, pronouns, verbs, adjectives, adverbs, and some conjunctions).

Lowercase the articles: the, a, and an.

Lowercase prepositions, regardless of length, except when they are stressed (i.e., through in A River Runs Through It).

Or, when used as adverbs or adjectives:
up in Look Up
down in Turn Down
on in The On Button

Lowercase the conjunctions: and, but, for, or, nor.

Lowercase the words: to and as just for simplicity’s sake.

Examples:
A Little Learning Is a Dangerous Thing
Singing While You Work
Tired but Happy
Taking Down Names, Spelling Them Out, and Typing Them Up
Sitting on the Floor in an Empty Room
Turn On, Tune In, and Enjoy.

Happy Writing!