Hello!!

First of choice filling won't increase your chances of getting admission. But yes do keep those colleges  with their branches in top priority which you think , it is little doubtful and you want that branch so that you can take it if you get it. Prioritise your preference in the order of your liking of branch and college. But remember don't forget to keep an alternative branch of a college which you are not sure you are going to opt for. If you keep an alternative, then you will atleast have a college by the end of the counseling session. Rest it's your wish you wanna opt of it or not.