Stream 1 : 70 % of seats through JEE (main) score and +2 Marks.

25 % and 75 % of weightage will be given to JEE score and +2 Marks under this stream. Your +2 Marks will be normalized with that of the first rank student's marks in your board. You will be ranked with respect to the combined score of your JEE (main ) and +2 Marks. Your rank will be determined by the combined scores of all other applicants.

Stream 2 : 30% of seats through +2 Marks.

You will be ranked according to the normalized percentage of your +2 Marks with other applicants under this stream.

Admissions under the two streams will happen according to your rank. You can apply under both the streams.

For more details about admission procedure visit this link

SASTRA University

Now, coming to your question. It is better to have a percentage of  about 97 to 98  or more in your board exams if you need to get into a branch of your choice. Your rank may vary according to the score of other applicants. So its always good topractice. .

Best  of luck