See there are different foundation courses available from different institutes such as Allen or pathfinder or Aakash etc. In those courses they develop Olympiad level preparation and provides you a foundation background for JEE ADVANCED which helps the student to grow in future. Now if you don't want to join classes then you can buy Pearson/Disha IIT JEE Foundation course books. you can read from this books and can ask your teachers question according to clear your doubts. This can also strengthen your preparation. So this are some of the ways you can follow, although a large number of student crack the examination by preparing from 11 as the syllabus of JEE ADVANCED is based on 11 and 12.

To know more about JEE ADVANCED visit the link below:

https://engineering.careers360.com/exams/jee-advanced

I hope this answer helps. All the very best for your future endeavors!