OHH don't worry first you have to learn some main topics like ATOMS, in rutherford's model of atom, Rutherford nuclear model, Spectrum and you shold solve some important numericals which you feel that this numerical is important and able to come on exam.
Now you should learn some important topics:-
1. Lyman series
2 Pfund series
3 Paschen series
4. balmer series
5 Brackett series
learn these topics carefully and best of luck for your exams.