Solve a specific real-world problem you have by writing a program to do it. Start with Python or Ruby. Start on one platform (Windows, Mac, Linux). Start small and get bigger by solving bigger problems as you progress.

Then, write a program that works on all major platforms with little or no modifications. Learn C++ or C. Learn how to use a debugger, how to distribute code to end-users, etc. While doing this, learn data structures, big O notation and why they are important when you need to scale. Learn how to handle threaded data safely and Unicode input too.

Just start coding ASAP to solve "real-world" problems (not book exercises), the rest will come as you progress.

Edit: Spelling