Revise.....revise.....revise Don't study anything new, if possible. Set yr body clock right. Ensure that u get up in the morning and feel fresh/are raring to go at the hours when IIT wd be conducting the test. No afternoon siesta when JEE wd be in progress.
Write at least 3 full fledged exams between now & 5th April....check out on the same day ( the day u take the test) where u went wrong. Take the tests at the same time that JEE wd be conducting the test. I repeat, synchronize yr body clock.
On 6th, check out all the mistakes u had made in the various tests taken by u during the course of the last 2 years.