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.
They are:
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
Source: http://www.allaboutagile.com/what-is-agile-10-key-principles/