Depends on the time of day.
When the MK is open, take the bus from the BW to the MK, and then get on the monorail for the GF.
If the MK is not open, you'll have to go through Downtown Disney.
There's always the options of walking through Epcot for the monorail (That takes a lot longer than you would think), or taking the boat or walking to MGM and getting a GF bus there (that's also a time consuming option.
You can always take a cab. Cab fare is about $15-17 including tip, depending on traffic.
Anne