I found this pdf presentation a while ago. This is not from me, but (therefore?) I find it absolutelly brillant! Joint placement is often ignored for the benefit of more complex and fancy setups. The truth is no matter how good your helper joints will be, they'll never bring you the same kind of natural look and flexibility than a joint placed correctly in the first place. I don't know under which licence this pdf is, I found it available publicly, but if you happen to know (or even better, to have a way to contact the author), please let me know.
If you want to download the original file, you can find it here