The first thing is one should not start new topics at the last minute. Rather, try to focus on what you have already prepared and have a strong hold on that.
Make short notes of the formulae and equations while studying which you can utilise to revise at the last minute.
Check the topics from which more questions will appear.
While there are many mock tests available online, solve them every day. But don't let those mock tests lower your confidence level.
Try avoiding studying too much one day before an exam. Conserve energy and try to stay as calm and confident as possible.
JEE is one of the toughest exams in India. Hence, it is very essential to have a positive approach to face the exam.