How much should I want to score in CAT to enroll into an IIM, especially in IIM Trichy, as I am from Tamilnadu? Is there any preference for female candidates?

The CAT cutoff for this year at IIM Trichy for the General Category is 

For female candidates, an extra 1% will be awarded in calculating your final total score for admission.

Despite the cutoff, a certain percentile cannot guarantee your admission. This is because the CAT score is a major but not the only parameter which constitutes the admission criteria. Other factors include the Personal Interview, Work Experience, Gender Diversity, and past academic records. Moreover, your rank also depends on the collective performance of your entire batch.