To go to the apartment from Shinagawa station, look for the Takanawa exit to get out of the station, then cross the road using the zebra crossing, head to the right and then turn first left, walk up the sloping street till you reach the traffic light junction. Turn left and walk about 50 metres and the property is on your right.
Other than a few spots on the carpet, the place is clean and comfortable.
The Narita express stops in Shinagawa, so no change of trains and it is really convenient.