Hi Surinder, while choice filling you must keep few points in mind:
1. Fill the choice based on your preference, for example, your preference order is first preference XYZ college and second preference is ABC college, so the same should be reflected on your choice filling they will be alloting based on your preference order of choice.
2 See all the good colleges based on your merit and if your merit is low then select colleges with little less ranking as well to make sure that you will be getting best college according to your merit and at least you are getting some college.
Hope this helps.