What can be done to crack the JEE (Advanced) and get into IIT-Bombay?

Don’t be fixed upon a certain agenda and keep your options open. If you will restrict yourself in such a way you might limit your options as well as the capacity to give your best.

Instead, I suggest that you try to analyze why exactly you want to pursue Engineering. Is it because of the sheep mentality or do you really want to build things?

Once you are sure, then figure out how exactly you will be achieving this goal. Set achievable goals for yourself and work sincerely on fulfilling them. Reward yourself for very little achievement on the way. This will gradually increase your confidence and pave the way to achieve much more.

However, a very important thing is to dream but not demand. That is you should be passionate about a certain thing but not fixated on it too much to the extent that if you fail to achieve it, you lose much more. So you can desire to pursue BTech in CSE at IIT Bombay but leave room for other options as well. 

Don’t stress yourself out too much and just concentrate on the present, your future will be visible sooner or later.