Try studying in chunks. Start trying to study 15 minutes without stopping, then 30 minutes a few days later, then 1 hour, etc. Take a 5 minute break between 15 minute study periods, then a 10 minute break between 30 minute study periods, then a 15 minute break every 1 hour of straight studying. Training your mind to stay focused is like training for a marathon; you cannot expect to study a whole day straight without working up to it.
Turn off/put away anything that distracts you, and make it inconvenient to regain access to it. I sometimes turn my cellphone off all the way bc if I wanted to get onto it I would have to sit and wait for it to boot back up.
When you need to take a long break, say for lunch/dinner, TAKE A LONG BREAK! I sometimes give myself 1 hour and 30 minutes for lunch or dinner. Also, try to give yourself 1 day off per week where you do NO STUDYING! I would usually take a day to do real-life stuff like laundry, cleaning, etc.
If you are reading a textbook with chapter objectives, try to write out the answers to the objectives as you read! It makes reading like a treasure hunt (I know lame, but you get it).
Vary your study methods. Try flashcards for a while, then textbook, then Qbank/textbook questions.
GET EXERCISE! Nothing is better than a nice run/bike/swim/sports game after a full day of studying. This will lower your stress and make you feel like you are accomplishing something outside of the library (getting in shape, being healthy, etc.)
That's all I got. Best of luck!
P.S.
Quotes from Bruce Lee in SDN forum signatures are also a source of inspiration.
