The purpose of this article is to summarise German declension as much as possible in the form of rules as distinct from tables. The idea is that only a minimum has to be learnt, and a maximum of regularities exploited. Well, the regularities are few and the rules are complex – but things are just not simpler. The question which case to apply when is outside the scope of this article.
This article contains a lot of detail which may be uninteresting for some or even most readers. It is designed for readers that have a fair basic knowledge of German and want an overview of the various intricacies of German declension, in particular of the influence the various parts of a nominal phrase can have on each other. For the resolution of a single question, not the entire article needs to be read:
For learning how German declension works without studying the details, you are invited to read the short first chapter on general principles in its entirety plus the introductory paragraphs of the subsequent two chapters, each up to the first subordinate headline. You might then want to glimpse at the examples before delving into the gory details.
For finding the pronoun and adjective endings in a sentence, make sure you know what strong and weak declension means, then jump to the chapter Declining The Entire Phrase. Read on until your question is answered, which will often be the case after much less than the entire chapter.
For finding the case endings for a given noun, there is a whole chapter on noun declension. But be warned, even with that one, you will need a dictionary because noun case endings can often not be found by applying rules.