hiii

Do not get demotivated. All you need is the dedication and honesty towards studies.
Try to cover all the important topics and also make a note of topics that are given more weightage to and start to study these topics properly. Do not waste time.
Try to clear all your concepts about any topic you have covered.
Give importance to all the three subject physics, chemistry and maths as in JEE all of them have equal weightage.
Practice Practice and Practice!!!
Note down all the formulas and important concepts so that they become handy for revision. Talk to your teachers they will be more than happy to help always and of course internet is always there. You can also post your questions on careers360 so that we can help you. 
Take online mock tests. 
Improve your calculation speed.
Keep on solving sample papers and previous year papers regularly and time all your papers so as to analyse your speed and result.
Focus on tricks to solve your questions rather than wasting time on lengthy calculations.
Don’t get upset and do not loose confidence if your score is less in earlier attempts as it would automatically gain a pace with time. keep practicing
Also I won’t advice you for late night studies, Sleep Early so as to keep your mind active and fresh.
And the most important advice don’t let anyone or anything break your flow.
Study with dedication and honesty, you will never fail

Hope this helps.
Thanks!

Hii Kalash...

Follow these steps and you will improve your marks and performance 

1) Buy a book having previous year papers (complete set) of JEE Mains. 

2) Buy one book of a good publisher with practice test papers (atleast 5-6).

3) Make a routine to solve the practice test one a day during 9 am to 12 am 

4) After the tests, check the answer key,Calculate your marks and analyze parts which you are constantly facing problem with. Read notes of these parts and try attempting them again.

5) Once you are done with the above point, read only notes and solve class notes question of the basic to average level.

6) Now that very less time is left, dont get started with anything new. You should always know, what you do not know

7) Try following a particular pattern for attempting the test i.e. PCM or CPM or MPC or any other. Thought best to go approach is CPM.

Hope this helps you. All the best.