I have done 12th in PCM with 71.8% what should i do
Your question does not seems clear. Do you want to increase your percentage or you want some suggestion regarding the colleges that you would be choosing for your Undergraduate studies?
In former case, you need to sit for improvement exams to increase your percentage.
As far as the college is concerned, for B.Tech , you have to sit for entrance exams.
While for B.Sc. you can apply directly to Universities like DU.
Do you want to enroll yourself in any skill enhancement course ?