Microsoft has a whole slew of sample projects, white papers, etc. covering best practices on a variety of topics. Many of these are focused on ASP.NET but you'll probably want to go right to the MS Best Practices center. They also published a book covering the topic but it is quite old and I wouldn't recommend it any longer.
Of course, you may want to go right to the source for an overall approach to coding best practices and for that I'd recommend Martin and Martin's Agile Principles, Patterns and Practices in C#. I'm just finishing up Robert Martin's Clean Code and, while a fair amount is obvious, it is well written, has tons of examples and has helped push me to be more "craftsmanlike" in my approach to coding.
The last thing is that I consider good Unit Testing to be one of the bedrock "best practices" for any developer. I recommend Pragmatic Unit Testing by Hunt and Thomas there.
That should get you going!