If the location is on the bus network from Heathrow, I suggest the guide linked in the second post to get to LHR and then the TFL journey planner to take a bus to the location from the Heathrow Central Bus Station.

If it's not, I suggest a local minicab (NOT the black cabs who will hate you for not giving them the lucrative fare back to central London they feel entitled to get from Heathrow) from a pickup point at the central terminals to the location.

If it's actually nowhere near Heathrow, then a taxi booked from LGW to the location starts to become more attractive especially with several people in your party.