The All About Agile site provides an interesting article about key principles in Agile Methodologies.
Here's a brief summary of the article.
From my use of various agile methods, I have written about 10 key principles of agile. These are characteristics that are common to all agile methods, and the things that I think make agile fundamentally different to a more traditional waterfall approach to software development.
1. Active user involvement is imperative
2. The team must be empowered to make decisions
3. Requirements evolve but the timescale is fixed
4. Capture requirements at a high level; lightweight & visual
5. Develop small, incremental releases and iterate
6. Focus on frequent delivery of products
7. Complete each feature before moving on to the next
8. Apply the 80/20 rule
9. Testing is integrated throughout the project lifecycle – test early and often
10. A collaborative & cooperative approach between all stakeholders is essential