If you are driving, the best way is to drive to the "Day lot" at Ft. Wilderness. If you are coming from the Magic Kingdom toll booth, it is the 2nd entrance on the left. If you are coming from the road past Port Orleans, it is the first lot on the right.
Once you park in that lot, then go to the bus stop just past the kennels, and take any bus marked "Settlement" (Purple, Yellow, or Orange). (These buses start at 6:40am) Get off at Settlement and walk toward the marina. When you pass Crockets Tavern, hang a left on the sidewalk towards Mickey's Backyard Barbecue.
If you wish to take Disney transportation, then take a bus to Magic Kingdom (buses to MK start at 6:30 am) then walk to the Contemporary out to their marina, then take a boat to Fort Wilderness. (These boats start at 6:45am) Then walk from the dock towards Pioneer Hall. Just before you get to Pioneer Hall, hang a right on the sidewalk towards Mickey's Backyard barbecue.