Concept projects are always a great way to learn and improve your design skills. It gives you the opportunity to try new things, ignore some constraints or really focus on particular areas you think you need to improve. A great example is the work that Aleksandr Maksimov shared on his Behance profile. It's a web design concept project for the Bjork web presence. It goes from desktop to mobile and it's beautiful. The grid is wisely used, there's a good amount of whitespace filled with bold typography and stunning imagery. There's a lot of issues too if you think about a responsive system, but I believe that wasn't the intention of the author here, it was more to explore the visual side of design.
Aleksandr Maksimov is a designer from Mykolaiv, Ukraine always seeking for new design challenges and ideas being concerned with achieving maximum client satisfaction and also creating a modern and unique look for every new project. For more information check out https://www.behance.net/aleksandrmaksimov