Mostly your 1st choice is given preference but then too it depends.You dont worry about that prepare well 

good luck

See you study for the exam dont worry about the center as of now you will come to know once admit card is out.There is 90 % chance that you will get your 1st choice of center.

see you will come to know once the admit cards are out.Mostly it depends on what date you filled the application form if you fill earlier chances of getting your desired center is more but the process varies.But mostly i guess the 1st choice is given preference.If you still not satisfied you can call on this

helpline number - 040-27070028

good luck