The green flash is best observed when you have a clear view of the horizon uncluttered by foreground objects and pollution free. This is primarily why stories of seeing the green flash frequently occur at the ocean. This is due to the additional amount of atmosphere one is looking through at the horizon when the Sun is setting. In addition, for approximately half the year the Sun sets over the ocean which is visible beyond the Los Angeles Basin. Because contamination in the atmosphere scatters blue light removing it from the line of sight.
More green light gets through and therefore is more clearly seen.
To best observe the Green Flash, it is important to know what to look for. Even though the Sun is near the horizon and attenuated from the increased atmospheric opacity, it is still very bright and concentrated observation with the naked eye or with optical instruments can be permanently harmful to eyesight. Observations should be made through heavily-smoked glass, welder's glass, or other neutral density filters. As stated before, the atmospheric conditions which are most favorable for the Green Flash are a calm and stratified atmosphere. The closer it gets to the horizon, the more flattened it gets.