Hello friend, At first focus only on JEE MAINS and not ADVANCED. ADVANCED preparation can easily be done in the 2 months time given after MAINS. I did it only in those months and that too for the last 10 days before JEE ADVANCED

HOW TO START:

Start with the most difficult subject you feel. Do it thoroughly daily for about 50% of you study time for 3 months. Side by side within the remaining time try to do the other 2 subjects. You should study for atleast 13 hours a day if you don't go to school And 6 hours during school days. If you go to any coaching do NOT completely rely on it. Do something side by side to supplement your preparation. Forget about excess playing or television, but you must have about 1 hour of divided entertainment everyday to maintain your focus. Complete your syllabus as soon as possible, and switch over to previous year papers( at least last 15 years). Do every paper at least 15 times (I did more than that). In my time, 2 questions were repeated “ as It is” in JEE mains and many questions in JEE adv were similar to those in last 10 year papers.

Practice for your speed .

Hello aspirant!!! You should prepare for 11th first and then study for 12th. Just go in a set sequence and follow that sequence. Mains syllabus is the same that is given in NCERT. So just follow the sequence that is given in NCERT. If you have joined a coaching then it is recommended to follow the sequence that they teach. Hope this helps. 

You should go on with both the classes and yess, do prepare the short notes for the same and reserve your last month only for previous year questions solving so that you can learn to pace up with the speed needed to solve the questions in the exams. 

Do keep a check on if you are solving quality questions as this matters alot.