by taxi, by autorickshaw, ciclorickshaw and the nice buses from old england. Just take the metro if you want to be faster and cheaper.
just to avoid confusion....the cycle-rickshaws have been taken off the streets of Mumbai and by Metro the author means local trains. also called mumbai's lifeline due to the lakhs of commuters who depend on these services on a daily basis. EXTREMELY CROWDED and not recomended for a new and inexperienced traveller.