Cut-off for JEE Advanced 2019 was -

General category : 100

Other Backward Classes (OBC-NCL) : 70

Scheduled Caste (SC) : 52

Scheduled Tribe (ST) : 48

So try to get more than 1/3rd of the total marks of the paper in JEE ADVANCED to get good branches like CSE, IT in probably the best IITS - IIT BOMBAY, IIT KHADAGPUR, etc.

Talking about JEE MAINS, toh from mains, you can only get admission into NITS, the cutoff for mains usually was around 39-45 marks. So you've to qualify JEE MAINS with a decent score and then score 1/3rd of the marks and above in Advanced ti ensure your seat in IITS.

Best wishes. Thank-you.