Hello,

You can start your JEE preparation in class 12th. Firstly, go through the syllabus of JEE and prepare yourself for it. Start preparing by studying for 3-4 hours and then increasing the time gradually. Practice JEE mocks and solve previous year's question papers for a better understanding of the paper pattern. This will also give you clarity about your strength and weakness of the topics. Make sure to clear all your doubts. There are various study materials available online that will help you in your preparation. Also, make sure to meditate and avoid stressing.

I hope this helps,

Thank you