Dos & don'ts for Kolkata travel:

For the international tourists, it is always advisable to carry their Indian visa, as it is cumbersome to get one after arriving
Carry all your important documents and money
If you are traveling alone, don't publicize it.
Incase you happen to lose your passport, immediately lodge a complaint at the police station and also inform your country's embassy.
It is advisable to carry adequate photocopies of your passport, traveler's checks and insurance.

Beware of touts and agents.
Make sure that your hotel reservation is done and it is confirmed.
To secure your belongings, use a combination lock.