What can I do to prepare for private pilot training? (India)
It's hard to give you specific advice for India because I'm not familiar with the regulations and standards there (your best bet would be to give the DGCA a call and ask if they have any publications you can review).

Broadly speaking all countries are going to expect you to know much of the same material however (because all airplanes essentially fly the same way). Along those lines, the FAA publishes some of the best flight training resources out there, and it's all available online for free.
I would recommend two of the publications to anyone considering flight training:


The Airplane Flying Handbook
This is where I'd generally suggest starting - a basic "How does all this flying stuff work?" textbook on a par with any of the commercially-produced materials.
Details on specific regulations, procedures, how to read charts, etc. may vary, but all of the material on aerodynamics, systems, flight controls, and maneuvers will be applicable.
If you're interested in helicopters there's a Helicopter Flying Handbook as well.
The Aeronautical Information Manual (direct PDF link)
This will be less useful to you as it's written with US regulations in mind (and stuff like aeronautical charting is probably different in India than it is in the US), but again there are large sections that are broadly applicable: Chapters 1, 2, and 8 in particular.


In addition to reading you can gain some experience using simulators if you use them effectively - even relatively inexpensive home simulation software &amp; equipment can be helpful, though it's not a substitute for the real thing. We've got a good Q&amp;A on using simulators to help in training which addresses some of the strengths and weaknesses of learning in a simulator. To help keep you from developing bad habits you would have to un-learn in a real airplane there are also companies providing what's effectively a private pilot flight course via simulators for free, and that will help you get started doing things right - following all the procedures as you would for a real airplane.