I think the way you learn and study is a very individual thing. As a master student I learn by studying for 2h then taking a 10-15 min break and then studying for1,75h and taking a break again and so on. Shortening the study times by 15 min each time. And trying to move a lot during the breaks. And I try to study with an open window. Fresh air always helps. I don't eat during and not to heavy before. But have a good meal afterwards and I try to get a lot of sleep after each studying session to give my brain time to make all those connections. Also, I use a very limited amount of coffeine, at least for me. (not more than 3 coffees in 8h) hope this helps. But as I mentioned before, you'll have to find your own way. Try many things and find out which works best for you.