The best way to attract them to your yard is to plant the flowers they love. Of course, location plays a role, too. I live in the city, kinda sorta, my friend is surrounded by woods. There will be more in a woodsy area than in the city. I planted a bunch of plants in a large bed last year to attract butterflies, bees, and hummingbirds, and the hummingbird's favorites in the bed seem to be the agastache -- sunset hyssop, monarda -- bee balm "Raspberry Wine", lobelia cardinalis -- cardinal flower, and I've seen them at phlox paniculata -- garden phlox (hummingbird moths like them too) and surprisingly I saw one feeding from delphinium exaltatum -- tall larkspur. Anything with red or orange tubular flowers will attract them, that's why the blue and purple flowers of the delphinium surprised me. Darn it, I need to go take some pictures.