EDIT: This answer was written for JEE(Main) 2018, although most points are the same as any other exams.

I’ll be telling some common mistakes during the exam(i.e.) tomorrow. Avoid each of these to score well. I have tried to order them chronologically. Read till the end.

1. Before entering the exam hall:

• Make sure you bring all your documents, admit card, etc and reach before time.
• Drink enough water, have adequate food(not too much), stop studying by 8 P.M. or so on a day before exam(have at least 7–8 hours of sleep).
• Go to the washroom before entering if you feel the need(you don’t want to go during the paper)
• . Many students study outside the exam hall. I don’t recommend that, and I also recommend ignoring such people if you aren’t one of them.
• Talk to your parents/guardian/teachers if they are present. Avoid talking to your ‘friends’. I remember my physics teacher saying that I should not worry, as he was pretty confident that I would do beyond expectations. These things ease out pressure.
• Be positive. It could be anything. I always listen to the song ‘Up&Up” for positivity before exam(don’t search for it now -_-).

2. In the hall before the paper is distributed:

• You would be given an OMR sheet. You don’t want to mess with it. Fill all the details.
• DON’T FILL THE DETAILS(SPECIALLY ROLL NUMBER) WRONG.
• Do not mess with the invigilators in any way.
• Make sure you have filled everything correctly. You would still have around 30 minutes before paper commencements.(don’t remember the sequence, it might be before OMR distribution).
• Now, avoid talking to people around you. They would be unknown mostly. A self talk helps at this time(I was pretty good at it :p).
• Relax and take heavy breath(and all that kind of shit), but don’t sleep.

3. After the paper is distributed:

• Don’t dive straight into the paper. Spend some time(5 minutes or so) looking at the questions. Try to get an idea as to what is tough and easy.
• Based on what is easy and what is your best subject, decide where to start.
• Attempt only a few easy questions in the beginning. Attempt 5–6 very easy questions from all the subjects first instead of attempting 20 questions from, say physics. This is where a lot of people go wrong. This builds confidence, as well as makes sure you attempt more.
• Don’t get stuck on a question for long. You can always do it later. This is a huge pitfall.
• Fill the OMR carefully and don’t keep it pending for end. That sheet shows years of hard work. If you fill it wrong or you could not fill it(i.e. the invigilator collects it before you fill it), then it would be real bad.
• Don’t answer without knowing(fluke).
• Choose the best option when in confusion. Don’t rely on ‘bonuses’.
• Use rough space wisely. It comes less in quantity.
• Solve fast, but don’t solve things wrong. Cross check quickly before bubbling, if its possible.
• Use objective approach whenever possible(specially in mathematics). Differentiating options, considering equilateral triangle, eliminating options should be used as much as possible.
• Don’t ever get depressed in between if you don’t get questions. It happened with me too. But I got up and gave a fresh start after 2 minutes. It’s very important.

3. After the paper is over:

• Head straight home, have lunch and chill for the day.
• Calculate your marks by evening. Stay happy and don’t get depressed or overconfident. I was scoring 350–360 from various keys. All were happy. but I went back to my books at night.
• Start preparing for JEE(Advanced) or any other exam.

I would recommend staying very positive and motivated. Don’t take any pressure. You all will get what you deserve. Give your best.

It’s your moment, squeeze it make it golden.

All the best.