ideally one should read 2 subjects the advantage of reading subject is you can increase the number of hours its one of the GAME CHANGING FACTOR while preparation giving more time. …as one usually get bored with one subject easily or its highy unlikely you can read one subject in a day like 10-12 hours… so keep 2 subjects …and in those 2 subject one should be your STRONG subject and one your WEAK subject…one should spend 2/3 rd of time to good subject and 1/3rd time to weak subject…in this way 10-12 hours you can read easily. so in a day while doing strong subject you get more confidence and when you do your weak subject you feel like you need to push more you will give more time towards it…make each everyday like it …as magic is in everyday efforts not few days few weeks before exam !