Ubuntu Wiki

1. The Ubuntu Packaging Guide

I'd probably say this is the best place to start, it's really good! The right amount of detail explained with a good deal of clarity

2. The Debian New Maintainers Guide

Much more comprehensive, a good read but also a good reference when you're looking for a specific explanation of something

3. Source Packages

With something in the region of 30,000 packages in ubuntu, if you want to package something theres more than likely going to be similar packages already in the repository. If you can find some then why not look at what others with similar programs have done, $apt-get source someprogram then rifle through their packaging, see if it suits your needs, and if so, use it as the basis for your own package

4. Ubuntu Developer Week

Why not learn from the experts!, there will be classes to help get started with packaging (and lots of other things) Previous developer weeks are archived so you can try them out when you have free time from the archives

More Useful Links

CDBS - Keep it simple and let the common debian build system deal with the finer points of packaging

Python Packaging Tutorial - A good walkthrough example of how to specifically package python programs