Psychology

You definitely need to create a "study spot". A study spot is somewhere in your house where the only thing you do there is study.
Your body and your mind associate activities with certain places. Studying in bed is a bad idea, because when you get in bed your mind thinks "sleep".
Studying in front of the TV is bad, because usually TV-watching is for when you are trying to relax. Studying at the dining room table can be bad, because sitting there usually means eating.
You need a very quiet place too. If your friends or family are being loud or they are watching TV or something nearby, you won't be able to concentrate.
Find a corner of your house, or a closet, or somewhere, where you can set up a small table or desk with a lamp. Don't play any music that has lyrics while you are studying, either, because lyrics are distracting. Don't do anything else at that desk except study.
Another good tip is to set a certain time for studying and stick to it. And don't start late at night if you can help it, since you will already be tired. For example, decide that every day when you come home from school you will study for 1 or 2 hours right away (in your quiet study spot). Give yourself some kind of small reward after every time you actually do this.
Once this pattern becomes a habit (might take two or three weeks) you won't be as distracted. Your mind and body will start to expect that at a certain time and place, you will study. It won't be such a big deal anymore.