For appearing in jee advance you have to score minimum 75% aggregate marks (that means in total ). You don't need to worry a lot about it .For good marks in boards you should strictly follow your ncert book it is quite helpful. To get acquainted with previous year question you should solve sample paper. There are many publication sample books are in the market. Bt personally I would suggest you for oswal.you should balance your both studies i.e for competition and for boards.

All the best for your exams