- Create a Launchpad account
- Read the Debian Policy Manual. It is a technical specification on how the packages are structured, and what each of the files in debian/ is for. At least the first 5 chapters are elemental knowledge. While you may not understand everything at first, it will give you some good base knowledge about Debian packaging. Bookmark it, so you can refer to it later.
- Set up your environment
The Ubuntu Packaging doc guides you through: