Dear frnd,

See, syllabus wise, there is little difference between 11-12th studies and IIT-JEE.What makes these two things different is the question pattern.But to tackle the tricky questions asked in the JEE you need to be thorough with the basics of each subject.So do your 12 th syllabus as quickly as possible (in 3 months time!).
In next one month revise your 11 th well.Then go in for extensive problem solving from all topics of the JEE syllabus-and all through this, keep revising the concepts and theory at periodic interval.Subscribe some Magazine that is focussed on engineering entrance.Solve test papers published in it.Don't ignore your normal 12 th studies.

After clearing class 11 and class 12th concepts, you should start solving entrance type questions in each subject from mock tests. Now-a-days, there are many websites that offer online