Notice in the video how the detectorist keeps his coil to the ground, makes a wide sweep covering lots of area and overlaps his swings.
Then notice in the second half of the video the demonstration of improper technique when swinging your metal detector. Many people, especially beginners, will use what is known as the "banana swing" when out detecting. This type of swing only covers a few inches of the ground per sweep, missing all sorts of potential targets.
The proper swing technique will cover the most ground and give you the most depth from your metal detector, therefore providing the most opportunity for good finds. I hope this video on how to use your metal detector with a proper swing is helpful to you.