Well normally admissions to DU are completely based on merit. However DU also give admissions to those who excell in extracurricular activties like in sports and arts. As you said that you have participated in state level, you could either apply for sports quota or ECA(extracurricular activites) quota along with our application form depending upon your talent. Please check the site and if you qualify the preliminary round authorites may check your skills in-person.

      Though cut off's vary each year, if you want get into DU  for UG programmes based on merit then you have to get around 90% in your class 12 exams. However even this cut - off's can also vary greatly and with colleges. Normally arts and commerce cources have greater cut -offs than science. Please do remember that cut-offs vary greatly with the courses.

       Moreover if you belong to SC,ST,OBC catergories or is physically disablled the chances for you to get into top DU colleges in greater. Moreover some courses provides relaxation to girl candidates. Moreover there is newly proposed reservation for economically weaker sections.

Hope that you will find this useful.

The merit list will be announced after the results of 12th are announced. The cut off will be then released by the official site of DU then. Every year it is different. But generally it lies between 90 to 93 % for the first merit list.  Your admission will be depending on the cut off list that will be released after result. 

Hope you find this useful.