I wish to pursue my MBA in a premier business school. Is it better to go straight from my graduation (B.Tech in CS) or get some work experience and then go on with MBA?
Usually, MBA is something that you do when you have significant work experience. There is a good reason for that. If you go straight from your graduation into the program, you will learn a few thing on the theoretical side of business administration. But if you already have encountered troubles in management, you will learn a lot from the numerous case studies (because most of the learning in a MBA is through case studies) and exchanges with other "students". Moreover, the main advantage of a MBA, besides the few things you learn, is the network that you will acquire, and only a few fellow students will be ready to network with somebody without experience.
I agree that the more practical working experience you have, the more useful your MBA studies will be. That being said, the purpose of the MBA and the related timing will also be important. I assume you want this MBA to further your career (move outside of the technical/engineering side of your work and into management, marketing, etc.). If you think the MBA is going to help you do that and you want to move into the business side sooner rather than later in your career then it might be advantageous start the MBA sooner, especially since your undergraduate degree is non-business.
It depends on the school I imagine, but when I did an MBA all of the students with non-business undergraduate degrees had to take a set of core business courses before being allowed to proceed on with MBA courses. If you were working during the day and going to school at night I imagine this would add some time to your total time in the program, so getting started early might be a good idea.
Additionally, if you have to pass a test to get into the MBA program (GMAT, etc.) then taking that soon after you graduate might be advantageous as you are still kind of in the "study mode" of school and preparing for the test will be simpler than if you let years go by without having taken an exam. You should check, but I believe the GMAT is good for X number of years after you take it so if you pass it early after graduating you can still wait a while before actually applying. You say you want to go to a top level school as well, so I imagine a high score on this test will also be important. Starting early if you think it will take a few tries to get that high mark would also be smart.
If you want to get headhunted or an “MBA salary” after you graduate you need work experience, at least 5 years. However if you want to build your company or move up the ladder later you can do it now.
The MBA is in no way theoretical, you may get more out of it with previous work experience, but you will acquire “real” work experience through study by cases and simulations. You get to solve real world problems, and that gives you experience. Also, a Business School is a microcosm of the working world and you have teachers/bosses to please, team-members/colleagues to manage, bureaucratese/paperwork to deal with, etc.
Many programs do accept MBA students straight from undergrad.
Networking? Vaguely heard of it but never experienced it, especially as a foreign student. Maybe that was real in the dark ages when there where 20 MBA programs in the world. Now when there is a B school behind every bush and corner I do not believe in such think as networking. Though I may be wrong especially at top universities MBA programs.