First, find out where your cell carrier's nearest tower is located. You can use a search engine to find one of the many tower location sites on the Web. Or you can download a tower-finder app.
Once you know the tower location, point the main center beam of the Yagi in the direction of the cell tower. Make sure the antenna radials are pointing up and down.
Display your phone's signal strength reading. Where to find the signal strength reading in your phone's menu tree varies by manufacturer, model and operating system. Consult the operations guide that came with your phone.
Or you can use a search engine to find the term "Signal Strength Reading' or 'Field Test Mode.' Or contact your phone manufacturer's customer service department.
Once the signal strength reading is displayed, connect the antenna to your cell phone. Pan the Yagi left and right in 10 degree increments until you get the best signal strength reading from your phone.
The signal strength reading is typically displayed in decibels (dBm). The reading is often displayed as a negative number, like -91 dBm, for example. But on some phones the - sign is omitted, so the reading displays as 91 dBm instead.
Regardless, a signal strength reading CLOSER TO ZERO is stronger. For example, a reading of -86 dBm (or 86 dBm) is stronger than -91 dBm (or 91 dBm).
When you pan the antenna, be sure to let go as you take a reading. If you are in contact with the antenna, it may give inaccurate readings.
Once you find the antenna position that provides the best signal strength, lock down the Yagi's position. You should now get optimum performance from your booster system.