In Verizon Access Manager, press Ctrl+D to bring up diagnostic mode. Then, enter diagvzw for the password. This will bring up a screen that shows the signal strength (RSSI) and signal-to-noise ratio (SINR). You want to aim the antenna to make the RSSI as close to 0 as possible (-40 is good, -90 is bad), and to make the SINR as large as possible (at least 5-10, higher if you can get it).
The panel antenna isn't as directional as a yagi, so you should be able to rotate it in 45-degree increments to get a good idea of the general direction that offers the strongest signal. After that, you can fine tune with smaller rotations.
You'll want to let go of the antenna and wait 15 or more seconds before looking at the signal strength to see if the direction is good.