First, check out patterns & practices - "Use Microsoft's proven practices for software engineering.".
Next check out IDesign: .NET Design and Process Solutions.
After you dig through those to get some ideas make sure to enable code analysis/FxCop on your code base. Start thoroughly going through each warning.
Last, but not least, go check out JetBrains' software and GET ReSharper. ReSharper (or similar tool, some are available out there) is a must have if you want to be 100% efficient and ensure you code to a high standard with a minimal amount of headache! :)
That will get you 99% covered on standards and best practices.
