So what should I fill first college according to my rank or some other college?

Dear aspirant

First of all I am explaining you in short the rule of choice  filling.During choice filling you can put any no of choices there and sort them according to your facvourable interest . In every round you will be allotted only one department of one college . According to your sorted choice list the top most available choice with vacant seats will be given to you . If you are happy with that then you lock that and get admission . Otherwise you upgrade. If any of the preceding choice's  seat  becomes vacant then you will get than otherwise you get the allotted seat given to you from the previous round. That's how it works. So choice filling and seat allotment is very vital.

So if you have already selected upgradation then you can't take admission now . Because if you get a new allotted seat then the allotted seat of the previous round will of be no use .

Admission can be done if you confirm the allotted seat given to you and don't upgrade further . Then you go to your respective institution with all the documents and get admitted.

So you must sort your choices according to your priority list. Like you should put your most favourite choice at the first position of thr list and then the 2nd favourite choice in the second position etc.

best wishes.