First i will prepare from ncert and through notes then i will try previous year jee main questions. Is it right ?

Go through chapter wise. Pick a single chapter and study the ncert book and then practice all the questions of that chapter from previous year question bank and ncert too.

May you suggest me the better books ? And how should i manage boards as well as jee main

When I was preparing I prefer book of DC pandey for physics ,hcv is also very good.
For maths and chemistry I prefer sample question banks ,and ncert is also important for chemistry.
To give regular test is good way to judge yourself.

Managing about jee and boards I would say if your solving hard question then easy is easy only .
Syllabus of board and jee is different but jee is little bit advance  .

But how should i prepare , only focus on class 12th boards or it is not enough for jee main?

Since you are not what done with the course of 11th you will need to put an extra effort for that taking up a coaching would be a good option, it will cover your class 11th and polish your 12th as well.Here only focusing on class 12th will make you score less in JEE main to score better you need to put an extra effort in class 11th course. The questions being asked in the boards are below the level of JEE main so while studying for class 12th will have to step Up it further and take into account the trend and the question types of JEE Mains and prepare accordingly. as I said coaching would be a good option for both class 11 and class 12th syllabus as well as JEE Mains.The schedule of your life for the year will become rigorous and will have to cope up with that without giving up, and keeping tabs on everything from school tests to coaching assignments. Also joining a test series would be a good option for evaluation of your performance and preparation level. 

Should i try from now with solving previous year questions ? And also please tell me where shpuld i go for coaching.

You can start observing the trends and solving papers anytime. But the sooner the better. You can take up coaching anywhere that suits your requirement. Most of the coachings are same. More depends on how you are taking it up and what your stratgistr are.