Photographers should try to work early in the mornings when the temperature is lower and butterflies move somewhat slower. The light is also generally soft and warm at this time of day.
Approach butterflies slowly and carefully to avoid any disturbance - even of the air around your body. Remember that butterflies still move to some extent even when at rest, and that the plants or flowers on which they settle may sway with the slightest breeze. Shutter speeds must of course be determined with a knowledge of what movement is likely to occur during an exposure, but in most cases a speed of 1/250 second should be fast enough to give a sharp image. Depth of field should be maximized by choosing an point of focus one third in to the depth of the subject insect.
It is always important to know what butterfly species is being photographed. Without this information, which should be properly recorded in the file name and metadata, it is unlikely that images can be sold or published. The identification process is made much easier these days because there is so much information published in books and on the internet. However, also remember to record where and when each shot was taken.