To start the preparation from the scratch, first complete your NCERT as the time is less try to focus on important topics only simultaneously keep doing sample papers and previous year papers. Try to cover them all within 20 days and keep rest 10 days for your online mocks. Try to give more number of mocks and check the test analysis report properly, work on your weak areas and be confident and do not cram.

Hope this helps!!!

Good Luck!!!