Hey Preeti,
There are many places to visit in Mumbai ... for your two days here are few -
Siddhivinayak temple
Haji Ali
Mahalakshmi temple
Worli sea face
Colaba
Marine drive
Nariman point
Elephanta Caves
Happy Travelling !!!
You can start day one at south Bombay exploring Gateway of India, Chattrapati Shivaji Museum, Colaba Causeway, Kaala Ghoda and then moving on to Marine Drive. Then you can explore bandra and bandstand at night.
On the second day you can visit one of the cleaner beaches like Aksa or Gorai. Then you can also visit the Vipassana Pagoda Temple.
Hi Preeti, here is a list of places you should definitely visit while on your trip to Mumbai
Marine drive
Gateway of India
Colaba Causeway
Juhu Beach
Siddhivinayak Temple
Haji Ali Dargah
Elephanta caves
Girgaum Chowpatty.
On your first day directly go to the elephanta caves in the morning and while returning back to the gateway of india stay there till evening and enjoy lighting at gateway, Taj mahal hotel and end your day with Girgaum Chwapaty view with dinner.
Second day visit mahalaxmi temple & haji ali located nearby than move towards worli Nehru planetarium & scenic view of worli seaface and moving towards taking Ganpati Bappa's blessings through Dadar worli sea link at dadar siddhivinayak temple.