first of all try to give maximum time in self study as much as possible. at least 8 hrs self study is must. also spend some time in meditation that improves concentration. whenever you are fresh study those topics which you find boring and difficult . whenever you feel sleepy study those topics which you find interesting or are weak. to avoid sleep take less diet. do not overeat. the less you eat less will be your sleep. eat fresh fuits, vegetables, juices(not artificial) as much as you can. take energy drinks like horlicks,boost etc. you can also take multivitamin tablets like revital or any other but under advise of doctor.