sir my gate score is 652.rank is 2242 and i belong to obc.which specialisation should i give first preference so that i can get into iit?

Hello Urooj, first of all congratulations on getting such a good score in GATE. Since your main motive is to get into IITs, check all the previous year's cut off trends and analyse
• in which IIT you want to go
• and if you can get admission into the course of your own choice there.

These are the links provided for checking those cut-offs:
1. IIT, Kharagpur
https://engineering.careers360.com/articles/gate-cutoff-for-iit-kharagpur
2. IIT BHU, Varanasi
https://engineering.careers360.com/articles/gate-cutoff-for-iit-bhu
3. IIT, Dhanbad
https://engineering.careers360.com/articles/gate-cutoff-for-iit-dhanbad
4. IIT Delhi
https://engineering.careers360.com/articles/gate-cutoff-for-iit-delhi
5. IIT Madras
https://engineering.careers360.com/articles/gate-cutoff-for-iit-madras
6. IIT Bombay
https://engineering.careers360.com/articles/gate-cutoff-for-iit-bombay
7. IIT Guwahati
https://engineering.careers360.com/articles/gate-cutoff-iit-guwahati
8. IIT Kanpur
https://engineering.careers360.com/articles/gate-cutoff-for-iit-kanpur
9. IIT Roorkee
https://engineering.careers360.com/articles/gate-cutoff-for-iit-roorkee
10. IIT Hyderabad
https://engineering.careers360.com/articles/gate-cutoff-for-iit-hyderabad
11. IIT Indore
https://engineering.careers360.com/articles/gate-cutoff-for-iit-indore
12. IIT Jodhpur
https://engineering.careers360.com/articles/gate-cutoff-iit-jodhpur
13. IIT Mandi
https://engineering.careers360.com/articles/gate-cutoff-for-iit-mandi
14. IIT Gandhinagar
https://engineering.careers360.com/articles/gate-cutoff-for-iit-gandhinagar
15. IISc Bangalore
https://engineering.careers360.com/articles/gate-cutoff-for-iisc-bangalore

IISc Bangalore has really high cut-offs so it's difficult to get that college. But you can also pursue civil engineering from IIT Guhawati as per the cut off trends. IIT Delhi can also be in your list.
All I can say is check all the possibilities and choose wisely.

Also you can use to the college predictor , to get some more accurate predictions about the colleges you can get. Check the link given below:
http://bit.ly/2J9S0MN

All the best!
I hope this helps.