Hi Shiva
MBBS being one of the toughest exams to crack, builds up a lot of pressure on the students. But keep your worries aside and follow the below mentioned tips:
1) Be thorough with basics in Physics, Chemistry and Biology of your Class 11th and 12th Board.
2) In addition to Objective Type Questions AIIMS MBBS Entrance Exam also has Assertion and Reason Type question in 3 subjects, Physics, Chemistry and Biology. One has to be thorough with the material.
3) Take Mock Tests as many as you can prior to one month before exam of same duration. This will settle you to hold examination for longer duration.
4) Revision is a must. Without revision you remember very less in the end of the month and almost things wash out completely in the end of the year. Make note of important facts and figures in topic wise manner and keep them revising on regular basis.
All the best 