[Haskell-cafe] The next 7000... abstractions to learn!

Hi all, I'm using Haskell since nearly three years now and I think I have well understood that types are the most important part of our programs. I have looked all around to learn as many datatypes/typeclasses as possible. But I suffer for a lack of direction to pursue my learning. I have well understood Prelude's one and some random ones (include someones for Category Theory), but I can't handle Kmett's code. Are there some intermediates abstractions I can learn? (For example in some librairies). Thanks by advance for your help. Regards.