There are two ways. If you are on kalimdor, go to ratchet and take the boat from there straight to booty bay.
If you are on eastern kingdoms...
If you have darkshire flight path, fly there, then head west through duskwood until you see a road that goes south. Take that road.
If you don't have darkshire fp, but do have sentinel hill fp, fly to sentinel hill and go southeast into duskwood headed east on the main road and you will come across the southern road to stv.
If you don't have sentinel hill or darkshire fp, walk from stormwind into westfall, and then into duskwood and follow above directions. Or you could cut through elwynn forest and northern duskwood.
If you have never been to eastern kingdoms, take the boat from darkshore to menethil harbor, follow the main road through wetlands and loch modan into dun morough. Continue following road and go to ironforge, take the deeprun tram in tinkertown, ironforge to stormwind, then follow above directions.