Back in 2009, I wrote a tutorial on the basics of packaging, up to using dpkg-buildpackage. This new version is steeper, and covers more ground. It is to be used partially at the Packaging Symposium held in Groningen November the 1st/2nd 2012. To learn packaging by example, this document should be a reasonable starting point. To be sure, there's a lot of other, excellent documentation to be found on the web. I mention two good examples here, but be sure to do a search:

However, a lot of the best and most extensive documentation is written more like reference material. This document doesn't try to be as complete, but it does try to provide practical, working examples.