One thing we should all note is that it is no longer acceptable to launch large-scale campaigns that target civilians as in WW1 and WW2, and that we also have nukes nowadays of course. If there is any chance of a WW3 happening, it probably has happened, either in the cold war, with indirect warfare between 2 factions: commies and cappies, each headed by its own superpower. stuff like Ogden, Korea, Nam, 73, 67, Afghanistan and many others just show us how said war was conducted: relatively by proxy.
The other candidate for WW3 would be the War on Terror, but that hasn't unfolded completely for me to really say much about.
Of course, if a 3rd (or 4th?) world war between China and India does happen, expect a lot of the same. They will not launch direct attacks against each other, but will start a series of proxy wars and attempts at dominating various key markets, and resource centers. Water will not be an issue, since the two countries are so saturated, so border wars and such probably won't happen.
We have to note, of course that stuff like that happening is unlikely, as China's economy focuses on things that India's economy does not, and vice versa. If stuff like this DOES happen, I expect the Chinese to emerge victorious. they have better infrastructure, and a more dynamic economy. India is running on 1950's infra. corruption in India is more of a problem that in China. stuff like that.