init.d script from usb

Hello - I like to find out how to start automatically my init.d script for my own brewn binary.

I noticed in " /var/media/ftp/external/etc/init.d " the external freetz ( eg rc.samba ) has been stored.
So initial thought was to put there my init.d script and to execute " update-rc.d " , so it will start automatically.
However that does not seem to be the correct way, is there a good howto I can follow please? Any hints welcome. cheers