I supplement this with reading a more advanced book which I understand little of and do not worry about understanding or applying, I find it helps keeps my mind engaged while working through banal exercises.
I have also found putting in the time to understand the long pedantic conversations/arguments some people have in various online forums to be quite valuable, they tend to be about nuances/minutiae of the language and this is something which books and the like fail to teach. This is actually what brought me to HN, when it comes to long seemingly pointless pedantry about code I have found no where better and I have learned a great deal from it.