Quick answers, from a casual fun-aggressive-builder Warlord-and-slightly-above player:
Your strength is your control of resources, so use that.
1. Use CivAssistII (an excellent utility, you can find it over on the Mods/Utilities forum if you don't already have it) to work out what resource India really needs most at the moment. If you combine the Technologies view (which tells you which civ has discovered what) with the "Miscellaneous" view, you may find out e.g. that India has Steam Power but no coal under its control. By denying them Coal you can prevent them from railroading (a Territory Map, if you can't see them, is useful here). Or, in another example, India may have Replaceable Parts but no Rubber. Deny them Rubber, and you'll only be meeting Riflemen as defence, rather than the Infantry of Doom...
2. Deny resources, but don't break any GPT deals you may have (even with India, who you mean to beat the hell of really soon!). Again, CivAssist can tell you (on the Current Trades screen) what your current deals are and how long they last. As soon as the initial 20 turns is over, you can break these deals with no repercussions - but do break them explicitly through a meeting, BEFORE declaring war.
3. Before invading, figure out what resource is most important for India to screw up your plans. It may be Saltpetre/Iron (in a pre-Riflemen situation), or Rubber (in a Replaceable Parts situation), or Horses. The CivAssist Miscellaneous view can show you where India is getting these things from (though not WHO they're getting them from, if they're importing them). Concentrate your war effort on pillaging and defending these crucial resource squares, and you'll make your life much easier.
I don't see CivAssist as a cheat - I see it as providing information that the game really should provide itself.