Sounds really cliché and obvious, but recreational time is just as important as study time! Taking breaks makes for much more effective study: try five to ten-minute breaks between every thirty minutes spent studying. Have some water each break and a snack every other (nut/oat bars are great...
It seems like such an obvious thing. but study with friends!
I mean, it's basic game theory: "two heads are better than one", after all, but it really does help to get another set of eyes (or several) on your work/notes/assignments. When we read stuff, it's easy for our eyes to miss typos...