Hi shatakshikaushal,
You ask a number of broad questions - and the best 'plan' for you will depend on which type of Degree best suits your Career goals. When it comes to defining the direction you want your Career to go in (and what you want your Degree to do for you), you might consider discussing those ideas with Senior Employees in your Company or other Professionals in your Industry who have a 'job' that you're interested in. With a specific 'outcome' in mind, you would be better able to reverse-engineer the path you would need to take to get to that outcome (and which Degree would be most appropriate as well as which Test you should take).
As far as the individual Exams are concerned, once you are ready to begin your studies, you can take a free practice GMAT (at
www.mba.com) and a free practice GRE (at
www.gre.org) to get a sense of your skills, strengths and weaknesses.
1) Even if you don't have any specific Schools/Programs in mind yet, have you thought about when you want to apply to School?
2) Assuming that you would need to study for at least 3 months, how many hours do you think you could consistently study each week?
GMAT assassins aren't born, they're made,
Rich