I'd say, most important would be biology. PCM would be similar for all, so making biology your strength would be awesome.
Honestly, I am not even a top ranker at my coaching, and usually rank about 7 (in fact, my coaching people decided to take special KVPY classes and did not consider me 'worthy' enough to do it, and advised me to stay away from it) , but I was one of the 2 KVPY fellows from our centre. What differentiated me was biology (of course I scored more in bio than in math lol), which is how I got past the toppers and scored 3rd best in aptitude test from our centre. Bio would most definitely help, perhaps even more than practicing math.
If you are confident of biology, then the other sections do not have high goals with them. But if you are going sans bio, be prepared to score amazingly well in PCM and still be unsure about your selection (True story).