Writing down things have never worked for me when it comes to subjects like History. I may read the notes but they are going to go through my mind and enter a seemingly empty world where the words are instantly burned and forgotten. The way that I find it most effective to learn things is talking out loud. Yes, I know there's probably crazy people that do this but it's what I find most effective. For example, say I have to study for a History exam that covers a 150 year time span. I would first list all of the things that occurred in chronological order, as well as an explanation pertaining to all of those points. Following that, I would literally read the points out loud like I was having a conversation with someone. (Yes I know, sounds like I'm crazy

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If however, you are studying for something like Mathematics or Physics, then you are not going to have any luck simply READING it. You cannot perform well in these subjects by MEMORIZING what you have to do, rather you must UNDERSTAND what is going on. There is no other way to succeed in those subjects other than simply practicing with ever more increasing in difficulty questions.
Also, take plenty of breaks, but do not get off track. Studying for long periods of time is effectively useless to me. If I study for something, I would break up the chunks and have a final review at the very end in order to ensure that the material that I covered stuck with me. If you study for 6 hours, chances are that the material you covered from hour 2-5 is going to be lost on you.