Anyone traveling to Mumbai should plan ahead and read about the city prior to arriving there. Knowing some basic facts about the area can help ensure a trip there is enjoyable, comfortable, and as safe as possible.

Visas – Anyone traveling to any part of India must carry a Visa which must be presented upon arrival. A tourist Visa allows a visitor to stay in the country for up to 90 days. However, many times tourists wish to temporarily leave India to visit other countries and then return. If this is going to be the case, a “double” or “triple” entry Visa should be obtained. Anyone wanting to stay longer than 90 days in India must fill out an income tax certificate upon departure.

The foreign national of following Nine countries can get a Tourist Visa on arrival with a maximum validity of 30 days with single entry facility by the Immigration officer at Delhi, Mumbai, Chennai and Kolkata Airports and NOT in any other Immigration Check Posts (ICP's).

1.Finland 2.Japan 3.Luxembourg
4.New Zealand 5.Singapore 6. Cambodia
7. Vietnam 8. Philippines 9. Laos
10.Myanmar 11.Indonesia  

Here is the official Immigration Bureau link for India Visa rules : 

Climate – Mumbai has 3 distinct seasons : June - Sep rainy seasons. It rains almost everyday in these 4 months. July is the rainiest month. Climate is very pleasant when its not raining in these 4 months. Oct - Nov are warm and humid months. Dec-Jan is winter -  the best time to be in Mumbai, the weather is the most pleasant (relatively) Feb-May are peak summer months in Mumbai where temperatures are easily around 30 degrees Celcius along with humidity since Mumbai is so close to the sea.

In general you will never need winter clothing in Mumbai since the temperatures are usually never ever below 18-20 degrees Celcius. Always pack cotton clothes keeping in mind the heat and humidity.

Food & Water – It is advisable that tourists never drink tap water while they are in India. Drinking non-bottled water can cause severe stomach problems and can ruin a trip.

A bottle of bottled water usually costs 0.50 USD (50 cents on a dollar) and should never cost more than 1 US Dollar. 

No one eats cold food in India, warm food is the norm and foreigners should always choose hot cooked food, in the street as well as restaurants with clean utensils.