There is no substitute for adequate revision in the educational system. As a student, if you have done your revision, there is no need to get stressed in an exam. You will find several mistakes which could have been avoided in varsity/college exams occur chiefly as a result of inadequate preparation of students. Below are common mistakes made in exams, how to avoid them, and answer the questions better.
Most students panic at the placement of exams time table. It is easy to panic especially if your first reaction is that you are unprepared to take an exam. It is important to calm down, have a reading plan, study beforehand than to jump in for a last-minute study. In the end, you should be able to find that out of five, you can answer three questions accurately and make a reasonable attempt at the others. Start every exams preparation with a plan and when you have finished it, go through the same process again for all other courses. This will help you calm down.
Most students fail not because they have failed to plan, but because such a plan in under planned. Under planning is when a student is focused on his general knowledge of a course and suggest possible exams questions he/she should expect in as exams without a proper guide. A proper guide in this context is in the use of past questions that can give you a clue to the kind of questions you should be expecting before the actual exams. Hence, students should thrive to procure past questions on a course because it will help a lot.
Failing to Practice your answers
It is admittedly much easier to practice solving past questions which include a shorter essay-type response. An essay usually needs to make an argument, and have a reasonable flow from start to finish. This requires planning and practice. Before you start writing your essay, take five to ten minutes to plan what you are going to include in each section, and how you will structure your argument, beginning with an introduction, followed by the body and conclusion. You do, however, need to be able to time yourself as per the scheduled time allowed per the exams past questions before the actual exams.
The same goes for multiple choice exams. Try to be aware of the time, and the number of questions to be completed, and ensure that you have practiced enough to complete the paper within the time allowed. Before you start writing, check the number of questions, and the amount of time you have. This will tell you roughly how long you have to complete each question. Just as a basic check, read back over what you have written at the end and be sure it makes sense. If you think you need improvement, go over the same process again until you are sure you are ready to sit for the exams.
Finally, if you tried these methodologies and are unable to relax due to some distractions, you can take some time out and try again later. You should never study solely amidst distractions. If you try to practice before the exams, check back and make sure that you are ready and convinced of making the exams, not in overconfidence but in a stable mind.