Plant Diversity and Variety are important:
Some plants provide nectar for the butterflies to feed on, while others are sources of food for the caterpillars. Your garden must provide both. Select plants with varying heights and overlapping bloom periods to provide year round nectar accessability. Use masses of color, purple, white, orange, red and yellow to catch their attention.
Provide a Water Source:
Fill a shallow dish with sand to approx. 1 inch from the top and add pebbles for the butterflies to land on & add water. Of course you can do the same kind of thing with a birdbath too. Water fountains are always a nice accent and a source of water for them at the same time too.
It is recommended that you do not use overhead watering that would hit your butterflies, or knock off the caterpillars. Use boulders and garden art for them to have things to perch on too.
Applying pesticides around your butterfly plants is not recommended.
Killing garden pests will also eliminate the the larva or caterpillars that will eventually turn into more butterflies.
Unfortunatly, You have to allow some leaf munching to have the butterflies.
Organic gardening is best in butterfly and hummingbird gardens as much as possible.