The first and the foremost thing is that BMC needs to be scrapped and a new civic authority with ultra modern technology should be in its place. As of now, there is a weak system in place at mumbai with absolutely no willingness on the part of civic authority to take any responsibility. Any new Civic authority should be accountable and responsible with a difference in attitude. Any lethargic old system is very difficult to move.
The second and the most important thing is slums have to be removed from complete mumbai. No matter what. Give them new houses or do anything u want but remove this slums. They are the major cause for failure of making any proper system in mumbai. Relocate the slum dwellers and remove all the slums will solve 60% of the mumbai problems.
Also the old building need to be reconstructed no matter what. Any building more than 25-30 years old should be rebuild keeping in mind the rising population of mumbai and problems within. IF they have financial problems of rebuilding increase the no. of floors and sell them but get your building reconstructed.The example can be followed through Nehru Nagar, Kurla.