Make sure you learn how to use and leverage Dependency Injection / Inversion of Control in your applications. Other very important pieces of software to learn to include with your development is Microsoft Enterprise Library and Windows Communication Foundation. Those 2 tools offer an amazing amount of leverage to avoid having to recreate the wheel to solve problems.
Other really good packages to become familiar with are NHibernate and Fluent NHibernate.
Windows Workflow Foundation is a very powerful piece of software however the complexity level is high this would be another great addition to your knowledge base time permitting.
