Pay more attention to your everyday life
Well you don't need to worry about not having a clue about what to build.There're many useful applications,like a guard system for your house or just an LED clock.Think of something inconvenient and see if you can solve it with MCUs.
Only knowing how to program MCUs is not enough.You always need peripheries in your MCU systems,so building a new system forces you,to learn how to use other components.This is a good thing.That's my opinion.
You can also view the previous posts in this forum,there're a LOT of ideas about whatever.You're likely to find what you need there.May you succeed.