Within Delhi, the Delhi Metro Rail network is the most efficient and economical means to travel to Qutab Minar and other heritage attractions like the Mehrauli Archeological Park.
There is a bus stop near Qutab Minar. Bus 502 & 533 connects Qutab Minar with India Gate.
Another popular way is to hire a cab. You can also hire an auto-rickshaw. Negotiate upfront the rates and waiting time.