Hi!
I have a very good link for you, it's a QA site with lots of advice on self-organization, like dealing with procrastination, time-management, and more.
http://productivity.stackexchange.com
I know this problem of losing motivation. But, believe me, it is not so difficult to deal with it! First of all, you should realize some things :
1) school is not as important as it seems. Most of the subjects may be boring, and you may even wonder : "Why on Earth do I have to do it? I won't need it in my future!" This is true. I am a student now, and recall my school years as ... well, useless.
2) But! What if you look at it from another point of view? Do you have a dream job? Do you want to go to university? Do you have any ambitions? Unfortunately, to achieve our goals we have to sacrifice something. If in your country good grades matter when you enroll at uni, then you have to be as determined as you can.
3) Determined, I said. But you don't need to make yourself do all the things you have to! I mean, be as flexible as you can. Try devoting less effort to the subjects you won't need in your life, and doing more carefully the tasks you will benefit from. E.g. what is the point in coloring geography maps for a teacher who doesn't even check them? Do it as quickly as you can, maybe ask your siblings to do it for you (if you have younger siblings, of course). The important thing is to see the difference between what you really need and what you don't, and to balance the grades so that they won't affect your future negatively.
4) The main point of having good grades is gaining self-confidence and the feeling of getting over difficulties! So, why not try to feel like a hero? To gain the feeling of pride? I mean, every day you can become a better person than you were yesterday! And this is cool, believe me.
OK, now it's time for tips!
1) draw/print a poster that describes your educational goals. You may make it as a diagram or a mind map, and cross the steps you have already completed. Put the poster on the wall and go on
2) Praise yourself for achieving small goals
3) Join an extra classes / interest group / some club, and try to make all the school projects that have more or less free topics to be devoted to that one interest! I.e. if you have to make a presentation on scientific topic for your society science class, and you like biology, try maybe presenting something about genetics, or medicine, or ecology? Or, if you like reading specific books, write compositions on literature classes and choose the material from those books! This will make the process of studying much more fun.
And last - everybody has their own way of studying. Bouncing a ball is OK I think. However, from my personal experience, when I really-really-really love the topic of my work, I can get completely absorbed in it, and don't want any distractions. Cause yes, concentration is important, I work much worse with music on. Maybe you could try getting rid of the ball bouncing for a while, just as an experiment.
