This page outlines the capitalization rules for the German language. It forms part of the MusicBrainz Capitalization Standard.
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).