It's easy. Take the SR-417 Greeneway (use south access road from the airport) west to exit 6. After getting off SR-417, go straight (west) on SR-536 past International Drive and SR-535. After the SR-535 intersection, get in the left hand lane and turn left into HIFS at the second exit about 1/2 mile past the SR-535 intersection.
On the HIFS website, they say to stay on SR-417 to exit 3, which is the Oceola Parkway. Go right (west) about 1/4 mile to International Drive south, turn right onto I-Drive, and go about one mile to the HIFS entrance on the left. It is about 17 miles from MCO to HIFS.
Either way works fine.