I'm sometimes find it really hard to concentrate, so I usually listen to music (any kind although classical gets me relaxed enough to work. Other people might find classical tranquilising though). I like studying with a friend because you can test each other, but sometimes, just before an exam, doing this can make you even more nervous.
I think the best advice I can give here is to take care of your health and try to get enough sleep. Sometimes, revision and studying can turn into a competition: who works the longest, who stays up the latest, who worries the most, who turns into a pile of poopie first. Seriously. People who study this way and take part in these "competitions" might make you feel like a slacker, but in the end, you'll be the one alert on exam day.
Hope this helps (=
xxx
~#OrangeJuice#~