I had a very hard time concentrating as well. What Waterbottle said is a very good idea. I would make a list of the things that were absolutely necessary (eg. papers that needed to be written) and start by just doing something from that list for 10 min. Then I would take a break - ideally go outside and get some fresh air and then go back to studying again. What also worked was forcing myself to study at the library because there weren't as many distractions ) Some people study easier in groups. I had a group of friends I studied with for some subjects. Each one of us would make a summary of a specific topic and share that among each other.