Hello Ananjan
If you are talking about the jee mains than you have to secure minimum 99 percentile marks to secure rank under 12 thousand .( May vary depending upon various other factors).
And percentile score is relative score depend upon the number of students who score more than you and total number of students .
Because even a student score 250 or 200 he/ she may have same percentile in both case when number of students who score more than 250 or 200 respectively are same .
So try to score best as you can .
Generally you need to score 230-260 marks  according to the previews of the January session.

Good luck