You have to first study 8-9 hours a day.
Practice daily.
Read your ncert textbook completely.
Practice previous years questions regularly.
Revise the topics that you have learnt though the five days of the week that is from monday to friday on every week ends.
Practise mock test regularly to know your strengths and weekness.
Clear your douts regularly .Do not keep it for later time , where in that case at the last moment you will not find time.
Practise the shortcut ways to find the square and cube roots of numbers, to find squares and cubes of numbers.