Atomic Structure is a very fundamental and easy chapter in JEE Chemistry. You don't need to mug up the concepts rather you should try to remember the formulas. In JEE there is hardly one question comes from this chapter. So read it as a fundamental chapter or base of other heavy chapter like Crystal Structure or Atomic Bonds.

Write all the formulas regarding n, l, m, s in a sheet and just watch it every week. Remember to watch and not to read. You should not read the formulas rather watch and try to recollect the fundamental concepts behind those.

Also make sure you grasp the concept of spdf orbitals. Take the chapter as base of Chemistry and you will definitely enjoy it. Watch youtube videos regarding fundamental concepts of atomic structure and read NCERT.

Hope you get my point. All the best.