It is very much achievable that you can score great marks and rank in 12th class and JEE Mains and JEE Advanced.

• The most important thing in the preparation is focus.So you need to understand how much can you focus each day.
• It would be good if you join some coaching it take some coaching material at home.
• For JEE-Mains in Maths and Physics solve more and more questions and try to increase your speed .It is not very difficult and is very scoring.
• In chemistry learn inorganic chemistry to your heart.Ten questions come from it .
• In JEE-Advanced understand concepts very deeply.Solve past papers repeatedly.
• In my preparation I have learnt focus is the key.So work on improving it.There are many good ways.

All the best!