1. You won't get them all no matter what so try for a tolerable level a la integrated pest management's economic damage criterion.
2. Yellow sticky cards will get some whiteflies but are more useful for monitoring infestation level, particularly the arrival of the first ones. The sticky cards will show the start of infestation before the pests become really obvious. In addition killing a few of the early ones is like swatting early flies before they have time for exponential proliferation.
3. Beneficial predatory insects can help kill some larvae but won't do a major part of the control job. Green lacewings and parasitic wasps (no stingers) are probably the most effective but are pretty mobile as adults. The praying mantis looks pretty neat but seems to be territorial enough to guarantee that they will not do a major insect control job. In any case most of the beneficials prefer aphids to whiteflies. If your neighbors have bought plants with whiteflies, there is a good chance they also bought some aphids.
4. Insecticidal soap spray is fairly effective on larvae but must contact them to be effective. Once infestation occurs, there will be more hatching every day. Spraying is needed every five to seven days. Soap sort of works on the adults if you get direct hits on their bodies. Good luck on doing that.
5. Other organic sprays such pyrethrum (from pyrethrum daisy petals) and rotenone (from a tropical root) will kill the larvae and adults on contact but also kill beneficial insects including pollinators. If you have to resort to these, spray near dusk to minimize contact with pollinating insects such as bees. Using more potent or persistent insecticides such as malathion or carbamate just increases side effects without killing many more whiteflies.
6. Systemic insecticides that make plant juices toxic work pretty well but should be used only on ornamentals for obvious reasons. If you have infected ornamentals such as fuchsia or coleus, use a systemic on them to help confine the problem.
7. Growing your own plants from seed as I do helps delay infestation. The whiteflies will come from neighbors even if you live in a neighborhood of single-family houses as I do.