My post on “Butterfly Gardening” gives much information on plant selection. In general, I suggest you provide flowers which provide nectar throughout the warm seasons and well into the fall of the year. Your garden site should be sunny to attract butterflies, so choose flowers which do well in a sunny location.  Try to choose plants which your butterfly guide books identify as host (food) plants for the caterpillars of butterflies known to fly in your area. Some of the “wildflower butterfly favorite” seed mixes available on the market have some good choices. For more specific plants to grow for caterpillar foods,  check out your guide books and some of my earlier posts on raising different species, e.g. spicebush swallowtails or regal moths.