Stand by the laser tripod. Aim the laser at the window. You should be able to see the reflection of the recieving equipment in the window. If not, reposition the laser or the reciever until you can. If it is dark out, turn a flashlight on near the reciever pointed at the window, that way you can see the reflection in the window and locate the laser appropriately.
Once the laser is aimed, look for the reflected beam/dot near the recieving station. White paper or cardboard (pizza boxes) can come in handy. Position the phototransistor in the beam.