Larvae Collect live larvae by sweeping aquatic habitats with a dip net. Anisoptera larvae are best kept in containers with a bit of wet moss or other vegetation to keep the humidity high. Hot water wrecks the caudal lamellae of Zygoptera, however. I prefer to keep exuviae dry and pin them through the base of the wing cases, placing a small drop of white glue at the point where the pin exits the base of the thorax ventrally.
Adults Use a long-handled aerial net.
White nets make it easier to find the specimen in the net. A large mesh may not be satsifactory if you're also collecting insects other than Odonata. The wings should be together above the back. If they are too large to go together in a single envelope, make certain that the fact they were mating is indicated on both envelopes. Place them in paper bags for a day or two so that the cuticle hardens and the colour pattern develops.