Years ago, as a c programmer who had done some Windows 3.1 programming, I learned a lot about object oriented design by using a development framework, specifically Borland's Object Windows Library. Their package back then also had a well-designed database object library for their database engine. Nowadays, all the database stuff is SQL, which does not lend itself to demonstrating, imho, good design.
So, my advice would be to do some programming of something you're a bit familiar with, making use of a well designed object library. I am not sure where to point you - Visual Studio is kind of huge, the Office object models are a little hard to get your hands around until you've spent some time with them...