Is fluency a measure of learning? Should you practice the same thing over and over again for a certain amount of time? How much time? Are you a good judge of whether you've learned something or not?
The Benefits of Interleaving Practice
From gocognitive.net: "One of the dilemmas facing a learner is the seductive nature of blocked practice. Performance improves fast and learning seems to be optimal - which is the reason why in many areas the idea of blocked practice - or focusing on one thing at a time - is so dominant. However, research has shown that the long-term effects of a more variable approach, where multiple things are practiced mixed together, are much more beneficial than blocked practice."