If you come from C and have just started C++, I assume you're also new to object oriented programming in general.

If you've mastered the basics (creating classes, objects, etc.), I suggest you learn about design patterns. There are sources on the internet, but the best source would be the book Design Patterns [Gang of Four].

This will teach you to program and think in an object-oriented way. Sure, it's not about Qt specifically, but I think it is important. Some design patterns are in fact part of the Qt library and learning about them will help you better understand the way Qt works.