Use camera in macro mode and if there is option for aperture adjustment choose the wide aperture for achieving details. In order to obtain shallow depth of field zoom your lens little to the extent not loosing details. Shoot in continuous focus mode as certain butterflies are very active. Try to be as close to the butterfly before making a shot. Try to frame them complete when they spread their wings. A frame with entire butterfly with wings spread out looks stunning with different patterns and colors. Capture butterflies in action by choosing a fast shutter speed or use sports mode. Always remember the key in butterfly photography is patience. Butterflies are very sensitive to movement and fly off on sensing some. Be patient and give them time to settle again.
To shoot Butterflies with Black Background visit : http://www.kumarss.com/2012/02/how-to-shoot-butterfly-with-black.html
My collection of Butterflies shot using Compact Canon Powershot SX 230 Hs