Hii, Raman 

The best chance to get a scholarship is through the school or college you study at,graduate students can work as assistants in exchange for full scholar ship at many high ranking universities like harvard often have generous financial aid programs for students from poor families,so your main challenge will be to get accepted to the university.Students that are highly talented academically or in practical skills such as sports also have a good chance to get scholarships,also look for scholarships in the country where you will be studying to find so just google out , foe example-scholarships for international students to the US,or rugby scholarships australia.Our home country as well provides some scholarships to study abroad like Tata scholarships for cornell university,rotary foundation ambassadorial scholarship and many more .Also to fetch any of the above scholarship you have to have the desired grades and qualification.Many a times you may have to give exam and then may get qualified to get one.