I find I-4 to World Drive then just following the signs to MK to be the easiest way to go to FW. Once you get to the gates at MK, stay to the far right, but not the last lane as it is buses only. Let them know you are checking in at FW. Once through stay to the right. You will turn right and then FW will be on your left.
Once on property, I do tend to use the back ways around more often than the main MK gate, but I do find it the easiest if FW is were I am headed first to go the direct route.