Once you get into the general area of WDW, follow the signs for the Magic Kingdom. You will actually go through toll booths at the parking lot entrance for MK. Go through one of the booths at the far right (when you tell them you are checking in to WL, they will wave you through and point you in the right direction). The road into the parking lot bends around to the left, but you will staying all the way to the right and driving roughly straight ahead (alongside and then under the monorail). At the traffic light, you will take a right into WL (left will take you to the Poly, SOG, GF and the TTC).
Hope this helps!
Mike