Butterflies are cold blooded and need the sun to warm their wings. For this reason, chose a site in full sun . Large rocks placed in the area provide warm spots for basking. You need to have protection from the wind for them. If this is hard for you to provide, plant your taller plants on the side with the greater amount of wind coming in.
Mud puddles are another requirement for obtaining necessary minerals.
When you are out watering keep a place muddy close by for the butterflies. If this is not possible, the same thing can be done by keeping a pan of wet mud in the butterfly garden. Reduce the use of pesticides in your garden. Butterflies and pesticides do not mix. Butterflies will lay eggs as they move around from garden to garden.