MBBS is the basic medicine degree in India and a number of other countries. The term MBBS stands for Bachelor of Medicine, Bachelor of Surgery. Admission to medical colleges offering MBBS degrees is done through entrance examinations. Such examination is based on questions from physics, chemistry and biology. The questions are multiple choice type (also known as MCQs).
Preparation for such entrance examinations ideally starts in 11th grade. It is good to know that you have already decided to start your preparations in 9th grade and hence will have the upper-hand over many applicants. The best (and the most obvious) suggestion would be to spend more time on science subjects. This can be done in one of the two ways: you can prepare yourself and use some of the textbooks and help books available for science or you can get enrolled into a number of coaching institutes for the same. The coaching institutes (such as Aakash, Allen, Bansal institute, etc.) specialize in training students specifically for these examinations. Many students prepare themselves and do really well in entrance examinations.
Ultimately, whether you study on your own or through coaching institutes, you will have to spend a large fraction of your time in preparation. Practice of multiple choice questions is also suggested. An important aspect of preparation is continuous revision. Ideally, one should revise every week or every other week. You can also use online tests (available on various blogs and forums) for practice. I would suggest simulating the test conditions and taking such tests. This would mean that you will be undisturbed for the duration of test.