What do core contributors need to know?

I’ll be working on an outline for the core contributor handbook in the coming weeks, so I figured I would start a brainstorming session here. Some potential questions to ask yourself:

  • What do core contributors need to know?
  • What would have been great to know when you first started getting involved?
  • What resources (such as pages on the Codex) have you found useful?
  • What do people (including/especially non-contributors) need to know about the development process/cycle/philosophies?