It's best to shoot Sassoon Docks before 9am before the activity almost completely fades and the sun is too high and fierce. While this is an extremely busy place before the sun even comes up, I think having the benefit of a rising sun and relatively low temperatures makes this locale a unique starting point for any south Bombay street photography.
There's one spot in particular here worthy of mentioning for first-timers. There's a dock next to the main fish market where the fishermen are typically tending to their nets, playing cards, sleeping, and loading/unloading their boats. You also have a great view of the main dock's end without having to fight the crowds to see where the fish auctions are held. It's a far cry from the frenzied masses just beyond and worth the trip just to have more of a personal interaction with fishermen.