Many local culture specific issues that faculty coming back from abroad after a long time may not know.
Address senior faculty (aged above 55, divisional chairmen, deputy directors, director etc.) as Professor X, unless they tell you otherwise.
Remember no one (faculty or administrative staff) can be fired. Therefore, request people to help you with the purchase, bills etc. Do not tell them it is their duty (it is a sure way for failure).
Some people will ask you personal questions (Why are you not married? You have been in the US but don't drink?). Do not be offended.
Ask senior faculty for advice. Many will be glad to help but will wait till you ask.
Remember that the only entitlement you have is salary (that is mentioned in the offer letter), if you think rest (start up grant, students, office, and lab space, which are not mentioned in the offer letter) are favors you are receiving, rather than you are supposed to get, your life will become more easy.
Bangalore is a laid-back metro city compared to many other Indian metro cities (most shops open after 10 AM and close by 8 PM), IISc is ten times more casual than Bangalore!.
IISc culture is more towards developing an independent research program by each faculty member, do not be offended when your colleagues do not respect collaborative work.
Do not be surprised about 'The easiest job becomes most difficult and most difficult job becomes easy'.
Indian administration has not matured to accept the electronic communication (e-mail is for information only), so writing a letter (hard-copy) is considered as the right way of communication.
"In India even the most mundane inquiries have a habit of ending this way. There may be two answers, there may be five, a dozen or a hundred; the only thing that is certain is that all will be different." -- Eric Newby
"India is a country where everyone is in a hurry but no one is ever on time".