There's really no trick to keeping them off. You just have to keep a good coat of wax on the car.
We had a similar bug at our home in California. I had a white truck and every time I washed it, there were these tiny little yellow dots that were a pain to get off. I sprayed my trees, I parked the truck in a different spot.....nothing worked. I did find that wetting the car and waiting a few minutes helped to soak into the spots and made them a little easier to remove. One day, after several years, they just went away. Never could figure out what caused them.
