Ideally students starts their preparation for JEE exam from class 10th as 2 years is enough to crack this tough exam.however if you wish to start preparations in class 9th you can do it by your own or taking some coaching classes but i dont recommend coaching at this age because they teach whatever you have taught in 9th class is basic concepts which is no use of in JEE exams .jee exam is only based on 11th and 12th syllabus and have advanced level.so for now try to focus on concepts that build strong base for further classes and participate in olympiads to Sharpen your mind.