Hold the lens up to one eye while closing the other one. This helps you focus all your attention on what you see through the lens without being distracted.
Shine a flashlight over the area where the glass broke. The light from the flashlight reflects off of the remaining glass shards and makes them more likely to be seen.
Lean down closer to the ground as you hold the flashlight in the same position. Get as close to the ground as you can and move the colored lens around to pick up reflections of light from the glass shards. The colored lens helps increase the contrast between the light reflection and the background, making the glass shards brighter as a result, but the shards must reflect the light at the right angle to be seen.