Avoiding your shadow on any insect is the key, but even more so with dragonflies. Also, for any animal, it's important to know their behaviour and sometimes physiology. For example, dragonflies tend to have better eyesight forward and above and it's pretty poor from below. This is due to an adaptation based on their hunting technique. Another trick that some advocate, is to slowly moving forward while waving from side to side, it is supposed to mimic a bush waving in the wind.