This portal discusses Debian Development.
The best way to get up to speed on what every Debian developer should know is to install the debian-policy and developers-reference packages, and read both documents. The Developer's corner on www.debian.org links to these and additional official project documents such as the New Maintainer's Guide.
http://www.debian.org/devel - Official Debian Developers information
Mentors are here to help
the Debian Bug Tracking System is the first place to know
if you find a bug in Debian, you will use reportbug
if you want to help Debian, you have to know about BugTriage
you can also participate to Bug Squashing Parties
it's good if you can submit patches
Linux kernel development
Other project discussions
LSB - Linux Standard Base
L10n - Debian Localization