I have a guest post, Lessons in Software from James Waletsky, on Shaping Software.  James is a Development lead at Microsoft, with several years of coaching teams on Agile practices and software engineering under his belt.  Here is a summary of his lessons:

• Lesson 1.    Keep it simple.
• Lesson 2.    Define ‘done’.
• Lesson 3.    Deliver incrementally and iteratively.
• Lesson 4.    Split scenarios into vertical slices.
• Lesson 5.    Continuously improve.
• Lesson 6.    Unit testing is the #1 quality practice.
• Lesson 7.    Don’t waste your time.
• Lesson 8.    Features are not the most important thing.
• Lesson 9.    Never trust anyone.
• Lesson 10.    Reviews without preparation are useless.

You can read an explanation of the lessons in his post, Lessons In Software from James Waletzky.