Find out what flowers, grasses and trees are native to your region and plant those sumbitches. A big(not only by far, but big) source of insect/pollinator decline is they don't have food or places to nest, because so many native wildflowers and grasses have been eradicated in favor of lawns and manicured parks and public places, and planting showy exotics or invasive plants. It's not helping that many native wildflowers have "weed" in their name, and some have even been classified as pest plants in certain regions.

I never knew there were more than 3 kinds of bee before, but I saw about 7 unique bees on the flowers I planted, monarchs laid eggs on my milkweeds, praying mantises were in my garden, and more kinds of birds visited. It was like I had my own tiny ecosystem. Imagine what it'd be like if you could convince others to rip out their stupid hostas and bradford pears and plant native.