From Pune station bus stand, please board the Shivneri going to Dadar. Deboard at Dadar and from there you will easily get taxis/Ola/Uber to Mumbai Central (if u have luggage). If no luggage, Dadar railway station is walking distance. Go to Western line and board a local towards Churchgate, getting down at Mumbai Central.
Personally, I would advise you to take cab to Mumbai Central from Dadar for convenience.