To improve Marks in JEE Main,

• Remain stick to the syllabus, 
• Read nothing outside it, study all the Topics Not your favourite,
• Don't just try to learn How to solve instead understand the concept properly and then solve the questions.
• In chemistry make short notes consisting of Important formula, Reactions and Mechanism and concept and read them once every day.
• For Mathematics solve different Types of Questions If you are able to solve certain kind of Problems then don't go for repeated Problems.
• While solving Problems solve them till the end even you know further steps How to solve because then only You will learn time management and certain Problems seems to be easy but they have many concepts hidden.

This are the few points make sure You implement all to see the difference.