Best technique for prolonged study
Since you have tagged it exams, let me offer some hints. I don't know what subject, so I'll assume something like math or CS.

The best way to study for exams is not to have to do it at all. That is to say, make sure that you know the answers to most of the questions likely to come up in an exam long before the date of the exam. 

In order to learn something deeply, you need to use repetition and feedback. The repetition means doing exercises, working problems, writing programs, etc. In other fields it might mean writing on topics of the course. The feedback part means that you have to get someone to comment on your work on the exercises. Normally that is the professor grading your work, but you can also use study groups to get feedback from peers (and give it to them as well). For some things you can use some form of automation to get feedback. 

But if your main technique is memorization it will likely be ineffective. It will be ineffective for most people, at least. It would be possible to memorize something like the complete text of a calculus book, for example, while actually understanding almost nothing and also not being able to solve anything beyond the easiest problems. Practice - reinforcement - and feedback. 

And you also want to give you brain a rest. You aren't a machine that works efficiently as long as it has fuel. Your brain needs periods of rest to actually allow it to synthesize the ideas that you are trying to learn. Pushing it constantly leads to less and less efficient working. Take a nap, or use physical activity to recharge.