From New York City. 
North on the Major Deegan to the NY State Thruway, over the Tappan Zee Bridge to Exit 12, or

North on the West Side Highway to the George Washington Bridge.  Take upper level and stay in right lane onto the Palisades Interstate Parkway.  Continue north on the PIP to Exit 9E (Thruway eastbound).  Take the Thruway one exit to Exit 12.  (This option is for non-commercial vehicles only).

From New Jersey.
North on the PIP, Garden State Parkway or I-287 to the New York State Thruway toward the Tappan Zee Bridge.  Take the Thruway to Exit 12.

From Upstate New York.
New York State Thruway to Exit 12.

From New England.
I-95 southbound to I-287 (Cross Westchester Expressway).  Take I-287 westbound to the New York State Thruway/Tappan Zee Bridge.  Go over bridge to Exit 12.

At Exit 12.
If northbound on Thruway, turn right at first light off the ramp, then stay to the left and turn left onto Route 303 northbound.

If southbound on Thruway, stay in extreme left lane on the ramp.  Turn left at the light and then turn left again onto Route 303 northbound.

On Route 303.
Proceed north on Route 303 two miles, passing two traffic lights in Valley Cottage.  A half mile past the second light, turn left into Clarkstown Executive Park at the next traffic light.  Near the end of the drive in, make the first left turn and then a quick right turn into the parking area.