Insecticidal soap . Make your own with dish soap . Google it. Neem oil works good to but costs more.

Yellow sticky cards.

Maybe you will just be lucky. Two years ago, they were an infestation........last year, nothing. Granted, I paid more attention to my plants last year. I think sometimes these things just go in cycles.

You can't prevent......you can only treat once they occur. The yellow sticky traps are great for indoor infestations but I have never found them to be very effective outdoors.

Insecticidal soap or neem oil work very well. If you make your own insecticidal soap, avoid dish soaps - they contain detergents and are often antibacterial. Look for castille soap instead.

Outdoors the yellow sticky cards also trap ladybugs. And lizards :(