What really helped me was the Microsoft certification program. In specific certificate 70-505. Though I never really took an exam I did read the self-paced training kit which helped me a lot in developing WinForm applications.
This is the book I'm talking about.[
^]
This site wraps up some topics.[
^]
Also, as someone already mention,
MSDN is a good place to start.[
^]
A very important aspect of any application is working with data. You should check out the 'Data development' topics, with a special interest in ADO.NET.
What will also help in building any application in .NET (or any Object Oriented language) is at least some knowledge of
SOLID, or Object Oriented Programming Principles[
^] which will make certain problems easier to solve by applying
Design Patterns[
^]. This stuff might seem pretty intimidating at first, but it's SO important to building good and maintainable software.
Of course there's a lot more to learn, but I think these should get you on your way. Oh, there is one thing you won't get from books. It's called "experience". Practice, practice, practice... Good luck!