Writing code that is easy read and test is not something that is easy to achieve. Unfortunately there are still way too much programming students who write awful spaghetti after graduating. But there is one really good book that helps you raise your code to new level – your code will be also communication tool for you and your fellow programmers.
Agile Principles, Patterns, and Practices in C# by Robert C. Martin and Micah Martin describes how to write software using C#. Book covers also most important design patterns and object-oriented development principles. There are very good, close to reality examples for every topic and that makes this book pretty easy to read and understand.