Many times, it happens with the students, they read the starting portion of the question and then assume the remaining and due to which they write incomplete or wrong answers. So, make this a habit to read the questions properly with a focused mind.
Just because you know the answer, you get excited and might write in hurry, and land up missing a few steps. So, even if you know the answer, review your answer properly for the question asked.
This is one of the most common errors by students. The step is right; the equation is correct but simply a wrong calculation. Students must work on this weaker area.
It is highly possible that in the actual paper due to stress or time constraints, you might copy wrong and then eventually give the wrong answer. So, recheck and tally the question/ equation from the question paper before you start solving it.
Eat a healthy diet and make sure that you do any outdoor physical activity like running, walking, cycling, etc. This will help you release anxiety and stress.
Do not overburden yourself with practicing till the last day, it will leave you pressurized. Simply pick up last year actual question paper and solve it in the allowed time lim it