Find a quite place to study. If this is not possible at home, try to use ares of your school during the day or your local library when you cannot use the school premises. Make sure that your study area is well lit and comfortable.
Sit at a desk. Very few people can study effectively in an armchair or in bed.
Work hard, but not so hard that you become overtired.
If you play sport or do regular exercise, do not stop. Just make sure that you fit this in around your studying and not the other way around.
Get enough sleep. Most people need seven to eight hours a night and you remember better if you are getting enough sleep.
You may need to neglect your social life for a while. Relax quietly with music or family rather than going out with friends, which could lead to late nights and poor concentration the next day.