Have a good schedule for completing all the syllabus which you have. Figure out how many days you have, to study the syllabus, and the subjects you have to read. Then make a schedule by dividing the days for each subject according to the subject's importance. In that way you can avoid tension because you know how much time you have to revise for each subject.

Sleep sufficiently. 8 hours of sleep is necessary for having a calm mind.

While you are studying, take a break when you are feeling tired and your mind starts to wander away. If your concentration does not last for an hour, you should take a 5-10 minute break every hour to refresh your mind. With practice and minimal distractions, you might be able to space out your breaks gradually, so you can study productively for longer stretches.

Exercise. This is one of the best solutions for avoiding tension. Do it every day.

Avoid junk foods, especially avoid meat, fried foods, chocolates and soft drinks etc.