my target is iit. how can prepare

Be regular, join a coaching if possible. It’s not compulsory, but gives you direction and a competitive environment helps a lot :) You can get your entrance level doubts cleared very easily. Focus on concepts first and then solve numericals based on those concepts to make sure you’ve understood it well. Practice lots of questions and following the pattern does help a lot. 

But also remember that you have to relax too, because stress will decrease your efficiency. 

Be regular and you’ll do well :)