I love to see butterflies soaring through the yard stopping from plant to plant to rest and get some nectar. I always go to the National Wildlife Federation for any information. I do this because they are there to help me and not sell me shit or having blinking pop up's when I least expect it. Like when I am reading about a topic I need to know more about. This site is reliable and non-profit!
Here is NWF link for their Gardening to attract butterflies .
Now back to the butterfly not only are they beautiful they have so many benefits for the yard.
They help to pollinate the flowers in your yard. You need to plant more then just the kind of flowers they need to eat. You would be wise to help them out by planting\things where they can lay there eggs, plant that they can use as food, plants for the larvae (caterpillar's) places to form chrysalises and nectar source for adults.
Here are some tips:
Plant native flower -there are different flowers for different area's.
I have a few butterfly bushes in my yard, some Yarrow plants and some Milkweed . All of these are great for my area I am in Zone 18 in Southern California you can find your zone by going here.
They love certain colors butterflies love red, yellow ,purple, orange and pink. They prefer flat and clustered flowers.
They love love love the sunshine. If you notice while you start to build your butterfly garden that most plant that thrive in the sun are native to your area and drought tolerant.
Plant so that when one plant dies off another will be blooming through the butterfly season
NO INSECTICIDES OR BUG KILLERS. This MUST be a natural garden.
Cater to your caterpillars
I hope this helps a little. I have a hill that I am planting just for butterflies and I will post as I create it. It should be fun and take a least one year but remember Rome was not built in a day!