hii i want to know that how to mange time for prepration of iit and school exams in +2? is coching is best option?

also i have problem that i am working hard but not getting more than 80% in +1 and +2 school exams but in 10 class i got 92%.

plese tell me any tips n tricks to study less for school and get more and more marks.

First of all, I just want to say that theres no short-cut to success. You cannot study less and score more. Obviously, it depends on your understanding....refer different books to understand the concept well and then, you can see your score getting higher.

About IIT coaching, I think it is very important(unless you can handle by yourself). Suppose you prepare only for 12th and get 90+, but after that you have to prepare for your entrance which will be difficult to prepare for, in short time.IIT coaching  helps you to prepare for almost all entrance exams. So I think you should go for IIT coaching and prepare for +2 board simultaneously.

Hope this helps.