Alison Riddell-Kachur wrote:
"7.127 In regular title capitalization, also known as headline style, the first and last words and all nouns, pronouns, adjectives, verbs, adverbs, and subordinating conjunctions (if, because, at, that, etc.) are capitalized. Articles (a, an, the), coordinating conjunctions and prepositions, regardless of length, are lowercased unless they are the first or last word of the title or subtitle. The "to" in infinitives is also lowercased. Long titles of works published in earlier centuries may retain the original capitalization, except that any word in full capitals should only carry an initial capital. No word in a quoted title should ever be set in full capitals, regardless of how it appears on the title page of the book itself, unless it is an acronym, such as WAC, UNICEF or FORTRAN.
7.128 Capitalizing hyphenated and open compounds in titles may be simplified by application of the following rule: First elements are always capitalized, subsequent elements are capitalized unless these are articles, prepositions, coordinating conjunctions, or such modifiers as flat, sharp, and natural following musical key symbols........."
This goes on for a while going into some pretty specific detail, but I guess the above ought to do you for now.
The New York Public Library's style guide says basically the same thing. Both are good style guides, and well worth the money.
Of course, not all books, magazines, or journals adhere to these standards. If you're the lucky one writing the rulebook, you could be revolutionary and minimalist by only capitalizing the first word in a headline and all proper names usually capitalized (for ex., John Wayne yes, e.e. cummings no). The Economist does it like that: see their website, www.economist.com.
Their style guide also has an exhaustive list of capitalized (and non-) names, organizations, etc., not in titles that you might find useful: http://www.economist.com/research/styleGuide/index.cfm?page=738525
But remember: "A balance has to be struck between so many capitals that the eyes dance and so few that the reader is diverted more by our style than by our substance."
If I may make one request that doesn't have to do with titles, since you're the one writing the rulebook: Please don't capitalize the word "internet". The Economist doesn't, the Financial Times doesn't, and it's becoming more and more popular not to (though many will give lots of very good reasons to do so). It's the "way of the future".