XP is really a refreshing change from the waterfall process. Some of the core practices include:

  1. Pair Programming - all production code is written in pairs.
  2. Unit Tests - all production code has unit test cases written for it.
  3. Do The Simplest Thing That Could Possibly Work - this means don't overengineer things.

Kent Beck's book is really worth reading if you are interested in learning more about Extreme Programming.

It has been said that the more you adopt eXtreme principles, the less "extreme" your project will feel.