When in doubt, the government printing office offers a helpful general rule. Capitalize everything except for “the articles a, an, and the; the prepositions at, by, for, in, of, on, to, and up; the conjunctions and, as, but, if, or, and nor; and the second element of a compound numeral,” such as One Hundred Twenty-three Years (if spelled out).
Note that prepositions of four letters or longer, such as from or among, are capitalized. Also, up, which is both an adverb and an adjective, can be an exception. Your government offers this example: “Built-Up Stockpiles Are Necessary (Up is an adverb here).”...
Huge pet peeve of mine. AP style rules or follow the trend and use "sentence case."