|Status: This is an official style guideline.|
Das erste Wort sollte groß geschrieben werden. Für den Rest gilt die übliche Groß- und Kleinschreibung.
Capitalize the first word of a title, and stick to the normal German capitalization rules for the rest of the title.
For non-German speakers the main rule of this document in short: Nouns (also "common" nouns, not only proper nouns) and the first word of a sentence/title are capitalized, everything else is not. This is not completely correct, but appropriate most of the time.
As noted in the Wikipedia article on Eszett, ß is the only European letter that does not have a corresponding capital letter (not yet, that is). Since it never appears at the beginning of a word, there is no need to convert ß to SS (or SZ) for capitalization. However, when correcting the capitalization of a title that is in all uppercase, it may be necessary to convert SS to ß (e.g. Rammstein's "WEISSES FLEISCH" should be capitalized as "Weißes Fleisch"). Please note that the use of ß has changed after the 1996 spelling reform (most important: new spelling dass and muss instead of daß and muß, but still ß after long vowels, e.g. groß, and after diphthongs, e.g. weiß).