If you are visiting the Gateway of India, do not miss the opportunity to see the Marine drive road or the Elephanta caves. There are ferry boats available to take you there.
Early morning is the best time to go as the crowds are down and the lighting is good for photographs.
If you're at City Palace, do visit the museum,the armory being the most interesting of its kind. Lots of opportunities to click photos there.
Remember to take snacks and water with you. No provision of buying these things inside, and humidity might leave you asking for it.
